, 2018

TO OUR STOCKHOLDERS:

You are cordially invited to attend the 2018 annual meeting of stockholders of Mateon Therapeutics, Inc., to be held at 10:00 a.m., local time, on Wednesday, June 20, 2018, at the offices of our counsel, Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., 44 Montgomery Street, 36th Floor, San Francisco, California 94104.

Details regarding the meeting, the business to be conducted at the meeting, and information about Mateon Therapeutics, Inc. that you should consider when you vote your shares are described in this proxy statement.

At the annual meeting, five persons will be elected to our Board of Directors. In addition, we will ask stockholders to approve the amended and restated Mateon Therapeutics, Inc. 2015 Equity Incentive Plan, to approve a proposed amendment to our Restated Certificate of Incorporation to increase the number of our authorized shares of common stock, and to ratify the selection of OUM & Co. LLP as our independent registered public accounting firm for the year ending December 31, 2018. The Board of Directors recommends the approval of each of the proposals. Such other business will be transacted as may properly come before the annual meeting.

Under Securities and Exchange Commission rules that allow companies to furnish proxy materials to stockholders over the Internet, we have elected to deliver our proxy materials to the majority of our stockholders over the Internet. This delivery process allows us to provide stockholders with the information they need, while at the same time conserving natural resources and lowering the cost of delivery. On approximately May 7, 2018, we will begin sending to our stockholders a Notice of Internet Availability of Proxy Materials (the “Notice”) containing instructions on how to access our proxy statement for our 2018 Annual Meeting of Stockholders and our 2017 annual report to stockholders. The Notice also provides instructions on how to vote online or by telephone and includes instructions on how to receive a paper copy of the proxy materials by mail.

We hope you will be able to attend the annual meeting. Whether you plan to attend the annual meeting or not, it is important that you cast your vote either in person or by proxy. You may vote over the Internet as well as by telephone or by mail. When you have finished reading the proxy statement, you are urged to vote in accordance with the instructions set forth in this proxy statement. We encourage you to vote by proxy so that your shares will be represented and voted at the meeting, whether or not you can attend.

Thank you for your continued support of Mateon Therapeutics, Inc. We look forward to seeing you at the annual meeting.

701 GATEWAY BOULEVARD, SUITE 210

SOUTH SAN FRANCISCO, CALIFORNIA 94080

NOTICE OF SPECIALANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON NOVEMBER 1, 2016JUNE 20, 2018

TO OUR STOCKHOLDERS:

The boardPlease take notice that the 2018 annual meeting of directorsstockholders (the “Board”“Annual Meeting”) of Mateon Therapeutics, Inc. (“Mateon” or the “Company”), a Delaware corporation, has called a special meeting (the “Special Meeting”) of stockholders, to propose a reverse split of our common stock in order to preserve our listing on The NASDAQ Capital Market. This is extremely important for a number of reasons, including, most critically, maintaining liquidity in the trading of our common stock for the benefit of all stockholders. Quite simply, if we do not take this action,which in no way changes your percentage ownership of Mateon, then our common stock is likely to be delisted by NASDAQ, which would likely significantly impair the valuation of our common stock and the entire company.

As you are aware through our previous communications, NASDAQ requires that the stock price of companies which trade on their systems have a closing bid price of at least $1.00 per share. As you are also aware, our closing stock price has not exceeded $0.90 per share in 2016, and has exceeded $0.80 per share only a few times – well short of the NASDAQ requirement. While we continue to work to build sustainable and long-term value for our business and core development programs, we cannot stake the future listing of the company on the hopes that our stock will trade over the closing bid price requirement within the next two months. Importantly, the reverse split will only be implemented if our common stock remains out of compliance with NASDAQ’s bid price requirements following the special stockholders’ meeting.

The Special Meeting will be held on Tuesday, November 1, 2016,Wednesday, June 20, 2018, at 2:10:00 p.m.a.m., local time, at the offices of the Company’s counsel, Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., 44 Montgomery Street, 36^th36th Floor, San Francisco, California 94104, for the following purposes:

1. To authorizeelect five members to the filingBoard of Directors to hold office until the 2019 annual meeting of stockholders or until their successors are duly elected and qualified;

2. To approve the amended and restated Mateon Therapeutics, Inc. 2015 Equity Incentive Plan, which includes an increase in the number of shares available for the grant of awards from 4,725,781 shares to 7,250,000 shares;

3. To approve a proposed amendment to the Company’s Restated Certificate of Incorporation to effect a reverse stock splitincrease the number of ourauthorized shares of common stock, $0.01 par value $0.01 per share, at a ratio infrom 70,000,000 to 150,000,000;

4. To ratify the rangeappointment of 1:2 to 1:4, such ratio within that range to be determined byOUM & Co. LLP as the Board of Directors consistent withCompany’s independent registered public accounting firm for the guidelines described in this proxy statement, and the filing of such amendment to be implemented, if at all, not later than November 27, 2016;

2. To approve the adjournment of the Special Meeting, if necessary, if a quorum is present, to solicit additional proxies if there are not sufficient votes to approve Proposal 1;year ending December 31, 2018; and

3.5. To transact such other business as may be properly brought before the SpecialAnnual Meeting and any adjournments thereof.

The Board of Directors and I recommendrecommends a vote for these proposals. I realize that many“for” the election of you have held our common stock for some timeeach director nominee and have been frustrated with the Company’s perceived lack of progress over the years. I understand and share this frustration, both as a stockholder myself and as a member of the Board beginning in 2007 – when, because I believed so strongly in the potential of our product candidates, I took my Board fees in shares of common stock instead of cash. I too have shared in the frustration of having my share ownership subject to a reverse stock split - twice. Because of my continued belief in the Company’s fundamental technology and prospects, and in order to work directly to turn the Company around, in May 2015 I accepted the challenge to become President and Chief Executive Officer of Mateon, knowing that changing the

Company’s direction would take time to accomplish properly – it always does. But I genuinely believe in the drugs we are developing, and I know from my own years of professional experience how to successfully develop drugs. For some more context, note that over the course of my career, I have reviewed clinical data from hundreds of investigational drugs, and have had the opportunity to evaluate the development of many of them in lieu of taking on those at Mateon. It is in this context that I became CEO at Mateon – not because I thought the process would be quick or easy, but because I truly believe in the significant potential of our vascular disrupting agents to benefit patients’ lives.

The current Board of Directors and I are steadfast in our belief that Mateon’s best days are ahead, and that we are pursuing the best course“for” vote for the development of our investigational drugssecond, third and increasing shareholder value. We are making important progress in all aspects of our business, although, unfortunately, this has not yet been reflected in the price of our stock. Important examples of our progress from the record date of our last shareholder meeting to today include:

As you know, at our last regularly-scheduled annual stockholder meeting, we proposed a reverse split of our common stock which did not receive your approval. We are now nearing the end of the second and final 180-day grace period that is provided under NASDAQ’s listing rules to regain compliance with the bid price requirement.We firmly believe that a reverse stock split andremainingfourth proposals listed on The NASDAQ Capital Market is in all shareholders’ best interests. Therefore, we are again asking for your approval to conduct a reverse split. Importantly, we have made a number of changes to the proposal based on shareholder feedback, including reducing the proposed ratio for the reverse split and committing to not execute the reverse split if in the interim our stock price is sufficient to re-comply with NASDAQ’s listing rules. The following table highlights key features comparing the previous proposal and the current proposal scheduled for vote on November 1, 2016:

In addition to the reverse stock split, there were other proposals at our annual meeting which did not receive shareholder support, and we are working to address the concerns that were communicated regarding each of these items, as well. For example, with respect to the directors, a majority of votes cast were “withheld” for our then-Chairman of the Board, who has a long affiliation with the Company, including approximately four years as our chief executive officer. As of August 17, 2016, this individual no longer serves as Chairman, has resigned from the Board, and is no longer affiliated with the Company in any capacity.

The Board of Directors and management team at Mateon are working diligently every day to increase shareholder value, but it is important to bear in mind that the development of investigational drugs requires time and persistence. As a management team, we began working for the Company full-time in mid-2015 with the goal of advancing our products as rapidly and cost-effectively as possible, and we remain firmly committed to this endeavor today. We also continue to pursue opportunities for a sale or license agreement with larger, better-financed entities that have interest in our vascular disrupting agents. We understand and have heard your concerns and are working to address them. We believe that we will be best positioned to build a stronger company – for the benefit of you, our shareholders – with a stock that remains listed on The NASDAQ Capital Market.

In closing, please note that we must consider the reverse splitnow because our stock will be subject to delisting if it does not trade over $1.00 per share for a minimum of ten consecutive trading days before November 28, 2016. To reiterate, I strongly believe that the value of the common stock, which you hold, will be meaningfully higher if we are able to remain listed on The NASDAQ Capital Market, andthis vote represents the last opportunity we have, which is fully under our control, to keep Mateon’s stock listed. Once again, if the reverse split is approved and implemented, every single shareholder in the Company, whether through ownership of common stock, warrants, or options, will participate equally.

I thank you for your continued support as a shareholder, and I look forward to providing you with updates and additional information as milestones are met.above.

The Board of Directors has fixed the close of business on September 15, 2016,April 30, 2018, as the record date for the determination of stockholders entitled to notice of and to vote at the SpecialAnnual Meeting and at any adjournments

thereof. You may vote if you were a record holder of Mateon Therapeutics shares at the close of business on this date. A list of stockholders of record will be available at the meeting and, during the 10 days prior to the meeting, at our principal executive offices located at 701 Gateway Boulevard, Suite 210, South San Francisco, California 94080.

All stockholders are cordially invited to attend the SpecialAnnual Meeting.Whether you plan to attend the SpecialAnnual Meeting or not, it is important that you cast your vote either in person or by proxy. When you have finished reading the proxy statement, we urge you to vote by following the instructions in the Notice of Internet Availability of Proxy Materials that you previously received and to submitsubmitting your proxy by the Internet, telephone or mail in order to ensure the presence of a quorum. You may change or revoke your proxy at any time before it is voted at the meeting.

September [●], 2016May 7, 2018

TABLE OF CONTENTS

PRELIMINARY COPIES FILED PURSUANT TO RULE14a-6(a)

701 GATEWAY BOULEVARD, SUITE 210

SOUTH SAN FRANCISCO, CALIFORNIA 94080

(650) 635-7000

PROXY STATEMENT FOR THE MATEON THERAPEUTICS, INC.

SPECIAL2018 ANNUAL MEETING OF STOCKHOLDERS TO BE HELD ON

November 1, 2016JUNE 20, 2018

This proxy statement, along with the accompanying notice of the Special Meeting2018 annual meeting of stockholders (the “Special“Annual Meeting”) of Mateon Therapeutics, Inc., contains information about the SpecialAnnual Meeting, including any adjournments or postponements of the SpecialAnnual Meeting. We are holding the SpecialAnnual Meeting at 2:10:00 p.m.a.m., local time, on Tuesday, November 1, 2016,Wednesday, June 20, 2018, at the offices of the Company’s counsel, Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., 44 Montgomery Street, 36th Floor, San Francisco, California 94104.

In this proxy statement, we refer to Mateon Therapeutics, Inc. as “Mateon, Therapeutics,” “the Company,” “we,” “our” and “us.”

This proxy statement relates to the solicitation of proxies by our Board of Directors for use at the SpecialAnnual Meeting.

On or about September 19, 2016,May 7, 2018, we will begin sending this proxy statement, the attachedImportant Notice Regarding the Availability of Special Meeting of Stockholders and the enclosed proxy cardProxy Materials to all stockholders entitled to vote at the Special Meeting.annual meeting.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE

STOCKHOLDER MEETING TO BE HELD ON NOVEMBER 1, 2016JUNE 20, 2018

This proxy statement isand our 2017 annual report to stockholders are being mailed to all stockholders of record. For stockholders that hold their shares in a brokerage account (also called “street name” stockholders), this proxy statement and our 2017 annual report to stockholders are available for viewing, printing and downloading at www.proxydocs.com/matn.www.proxyvote.com. To view these materials, please have your16-digit control number(s) available that appears on your Notice or proxy card. On this website, you can also elect to receive future distributions of our proxy statements and annual reports to stockholders by electronic delivery.

Additionally, you can find this proxy statementa copy of our Annual Report on Form10-K, which includes our financial statements for the year ended December 31, 2017, on the website of the SEC, at www.sec.gov, or in the “SEC Filings” section of the “Investors & News” section of our website at www.mateon.com. You may also obtain a printed copy of this proxy statement,our Annual Report on Form10-K, including our financial statements, free of charge, from us by sending a written request to Mateon Therapeutics, Inc., 701 Gateway Boulevard, Suite 210, South San Francisco, CA 94080. Exhibits will be provided upon written request and payment of an appropriate processing fee.

The SpecialAnnual Meeting will be held on Tuesday, November 1, 2016,Wednesday, June 20, 2018, at 2:10:00 p.m.a.m., local time, at the offices of the Company’s counsel, Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., 44 Montgomery Street, 36th Floor, San Francisco, California 94104. You mayare urged to attend the SpecialAnnual Meeting and vote in person. If you are unable to attend the Annual Meeting and vote in person, although we urge all stockholders to vote prior to the meeting. The Board of Directors would appreciate your prompt vote either electronically via the internet, viaInternet or telephone or via regular mail, and strongly encouragesmail. We encourage you to vote electronically, if you haveare given that option.

IMPORTANT INFORMATION ABOUT THE SPECIALANNUAL MEETING AND VOTING

Why is the Company Soliciting My Proxy? You received this proxy statement and the accompanying Notice of SpecialAnnual Meeting of Stockholders because our Board of Directors is soliciting your proxy to vote at the SpecialAnnual Meeting and any adjournments of the SpecialAnnual Meeting. This proxy statement along with the accompanying Notice of SpecialAnnual Meeting of Stockholders summarizes the purposes of the meeting and the information you need to know to vote at the SpecialAnnual Meeting.

We have made available to you on the Internet or have sent you this proxy statement, the Notice of SpecialAnnual Meeting of Stockholders, and the proxy card and a copy of our Annual Report on Form10-K for the year ended December 31, 2017, because you owned shares of Mateon Therapeutics common stock on the record date, September 15, 2016.April 30, 2018. The Company intends to commence distribution of the Important Notice Regarding the Availability of Proxy Materials, which we refer to throughout this proxy statement as the Notice, and, if applicable, the proxy materials to stockholders on or about September 19, 2016.May 7, 2018.

Why Did I Receive a Notice in the Mail Regarding the Internet Availability of Proxy Materials Instead of a Full Set of Proxy Materials? As permitted by the rules of the U.S. Securities and Exchange Commission, or the SEC, we may furnish our proxy materials to our stockholders by providing access to such documents on the Internet, rather than mailing printed copies of these materials to each stockholder. Most stockholders will not receive printed copies of the proxy materials unless they request them. We believe that this process should expedite stockholders’ receipt of proxy materials, lower the costs of the annual meeting and help to conserve natural resources. If you received a Notice by mail or electronically, you will not receive a printed or email copy of the proxy materials, unless you request one by following the instructions included in the Notice. Instead, the Notice instructs you as to how you may access and review all of the proxy materials and submit your proxy on the Internet. If you requested a paper copy of the proxy materials, you may authorize the voting of your shares by following the instructions on the proxy card, in addition to the other methods of voting described in this proxy statement.

Who Can Vote. Record holders of our common stock at the close of business on the record date, September 15, 2016,April 30, 2018, may vote at the SpecialAnnual Meeting. On September 15, 2016,April 30, 2018, approximately 23 record holders held 26,544,934 shares of our outstanding common stock. Our common stock is our only outstanding class of voting stock.

You do not need to attend the SpecialAnnual Meeting to vote your shares. Shares represented by valid proxies, received in time for the SpecialAnnual Meeting and not revoked prior to the SpecialAnnual Meeting, will be voted at the SpecialAnnual Meeting. For instructions on how to change or revoke your proxy, see “May I Change or Revoke My Proxy?”below.

How Many Votes You Have. Each share of our common stock that you own entitles you to one vote.

How You Can Vote. You can only vote your shares if you are either present in person or represented by proxy at the SpecialAnnual Meeting. Whether you plan to attend the SpecialAnnual Meeting or not, we urge you to vote by proxy. All shares represented by valid proxies that we receive through this solicitation, and that are not revoked, will be voted in accordance with your instructions on the proxy card or as instructed via Internet or telephone. You may specify whether your shares should be voted for or withheld for each nominee for director, and whether your shares should be voted for, against or abstained with respect to each of the twoother proposals. If you properly submit a proxy without giving specific voting instructions, your shares will be voted in accordance with the Board of Directors’ recommendations as noted below. Voting by proxy will not affect your right to attend the SpecialAnnual Meeting. If your shares are registered directly in your name through our stock transfer agent, American Stock Transfer & Trust Company, LLC (“AST”), or you have stock certificates registered in your name, you may vote:

If your shares are held in “street name” (held in the name of a bank, broker, or other holder of record), you will receive voting instructions from the holder of record. You must follow the instructions of the holder of record in order for your shares to be voted. Telephone and Internet voting also will be offered to stockholders owning shares through certain banks and brokers. If your shares are not registered in your own name and you plan to vote your shares in person at the SpecialAnnual Meeting, you should contact your broker or agent to obtain a legal proxy or broker’s proxy card and bring it to the SpecialAnnual Meeting in order to vote.

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Telephone and Internet voting facilities for stockholders of record will be available 24 hours a day and will close at 11:59 p.m., Eastern Time on October 31, 2016.June 19, 2018.

Recommendations of the Board of Directors.

The Board of Directors recommends that you vote:

If any other matter is properly presented, the proxy holdersholder will vote your shares in accordance with theirhis or her best judgment. At the time this proxy statement was first made available, we knew of no matters that needed to be acted on at the SpecialAnnual Meeting, other than those discussed in this proxy statement.

May I Change or Revoke My Proxy? If you give us your proxy, you may change or revoke it at any time before the SpecialAnnual Meeting. You may change or revoke your proxy in any one of the following ways:

Your most current vote, whether by telephone, Internet or proxy card is the one that will be counted.

How to Vote if You Receive More Than One Proxy Card. You may receive more than one proxy card if you hold shares of our common stock in more than one account, which may be in registered form or held in street name. Please vote in the manner described under “How“How You Can Vote”Vote” for each account to ensure that all of your shares are voted.

How Your Shares Will Be Voted if You Do Not Vote. If your shares are registered in your name or if you have stock certificates, they will not be counted if you do not vote as described above under “How“How You Can Vote.” If your shares are held in street name and you do not provide voting instructions to the bank, broker, or other nominee that holds your shares as described above, the bank, broker, or other nominee that holds your shares has the authority to vote your unvoted shares only on the proposals authorizing the amendment to the Company’s Restated Certificate of Incorporation and on the ratification of the Charter to effect the Reverse Stock Splitappointment of our independent registered public accounting firm (Proposals 3 and authorizing the adjournment of the Special Meeting to solicit additional proxies if there are insufficient votes to approve the amendment of the Charter to effect the Reverse Stock Split (Proposals 1 and 24 of this proxy statement) without receiving instructions from you. Therefore, we encourage you to provide voting instructions to your bank, broker, or other nominee. This ensures your shares will be voted at the SpecialAnnual Meeting and in the manner you desire. A “brokernon-vote” will occur if your broker cannot vote

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your shares on a particular matter because it has not received instructions from you and does not have discretionary voting authority on that matter or because your broker chooses not to vote on a matter for which it does have discretionary voting authority.

Your bank, broker, or other nominee does not have the ability to vote your uninstructed shares in the election of directors or the approval of the Amended and Restated 2015 Equity Incentive Plan. Therefore, if you hold your shares in street name it is critical that you cast your vote if you want your vote to be counted for the election of directors and the approval of the Amended and Restated 2015 Equity Incentive Plan, as disclosed in this proxy statement (Proposals 1 and 2 of this proxy statement).

Confidentiality of Votes. We will keep all the proxies, ballots and voting tabulations private. We only let Mediant CommunicationsBroadridge Financial Solutions, Inc., which is assisting us with our proxy process and serving as our inspector of election (the “Inspector of Election”), RR Donnelley, which is assisting us with our proxy process, AST our proxy solicitor, Morrow & Co., LLC, and other members of the Company’s management team examine these documents unless further disclosure is necessary to meet legal requirements.

Voting in Person. If you are a stockholder of record and plan to attend the SpecialAnnual Meeting and vote in person, we will give you a ballot when you arrive. However, if your shares are held in the name of your broker, bank, or other nominee, you must bring an account statement or letter from the nominee indicating that you were the beneficial owner of the shares on September 15, 2016,April 30, 2018, the record date, for determining who is entitled to vote.vote, and you must also make arrangements with your bank, broker or other nominee in advance so that our Inspector of Elections is able to verify that your shares have not been previously voted.

What Vote is Required to Approve Each Proposal and How are Votes Counted?

What Are the Costs of Soliciting these Proxies? We will pay all of the costs of soliciting these proxies. Our directors and employees may solicit proxies in person or by telephone, fax or email. We will pay these employees and directors no additional compensation for these services. We will ask banks, brokers and other institutions, nominees, and fiduciaries to forward these proxy materials to their principals and to obtain authority to execute proxies. We will then reimburse them for their expenses.

We have engaged Morrow & Co., LLC to act as our proxy solicitor in connection with the proposals to be acted upon at the Special Meeting. Pursuant to our agreement with Morrow & Co., LLC, they will, among other things, provide advice regarding proxy solicitation issues and solicit proxies from our stockholders on our behalf in connection with the Special Meeting. For these services, we will pay a fee of approximately $7,500 plus expenses.

Quorum. The presence, in person or by proxy, of the holders of a majority of the outstanding shares of our common stock is necessary to constitute a quorum at the SpecialAnnual Meeting. Votes of stockholders of record who are present at the meeting (in person or by proxy) and abstentions are counted for purposes of determining whether a quorum exists. If a broker has voted on at least one agenda item, then brokernon-votes are counted for purposes of determining whether a quorum exists.

Where to Find the Voting Results of the SpecialAnnual Meeting. The preliminary voting results will be announced at the SpecialAnnual Meeting, and we will publish preliminary, or final results if available, in a Current

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Report on Form8-K within four business days of the SpecialAnnual Meeting. If final results are unavailable at the time we file the Form8-K, then we will file an amended report on Form8-K to disclose the final voting results within four business days after the final voting results are known.

Householding of Annual Disclosure Documents. Securities and Exchange Commission (“SEC”)SEC rules concerning the delivery of annual disclosure documents allow us or your broker to send a single set of our proxy materials to any household at which two or more of our stockholders reside, if we or your broker believe that the stockholders are members of the same family. This practice, referred to as “householding,” benefits both you and us. It reduces the volume of duplicate information received at your household and helps to reduce our expenses. The rule applies to our annual reports, proxy statements, and information statements. Once you receive notice from your broker or from us that communications to your address will be “householded,” the practice will continue until you are otherwise notified or until you revoke your consent to the practice. Stockholders who participate in householding will continue to have access to and utilize separate proxy voting instructions.

If your household received a single set of proxy materials this year, but you would prefer to receive your own copy, please contact our transfer agent, AST, by calling their toll free number,1-800-937-5449.

If you do not wish to participate in “householding” and would like to receive your own set of Mateon Therapeutics’Mateon’s proxy materials in future years, follow the instructions described below. Conversely, if you share an address with another Mateon Therapeutics stockholder and together both of you would like to receive only a single set of proxy materials, follow these instructions:

Electronic Delivery of Company Stockholder Communications. Most stockholders can elect to view or receive copies of future proxy materials over the Internet instead of receiving paper copies in the mail.

You can choose this option and save the Company the cost of producing and mailing these documents by:

Attending the Special Meeting.Annual Meeting. The SpecialAnnual Meeting will be held at 2:10:00 p.m.,a.m, local time, on Tuesday, November 1, 2016Wednesday, June 20, 2018, at the offices of the Company’s counsel, Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., 44 Montgomery Street, 36th Floor, San Francisco, California 94104.

PROPOSAL 1: ELECTION OF DIRECTORS

Our Board of Directors currently consists of five members, including four members who are“Non-Employee Directors” within the meaning of Rule16b-3 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”). Under our Amended and RestatedBy-laws (the“By-laws”), the number of members of our Board of Directors is fixed from time to time by the Board of Directors. On April 18, 2018, our Board of Directors accepted the recommendation of the Nominating Committee and voted to nominate for election Dr. David J. Chaplin, Dr. Simon C. Pedder, Mr. Donald R. Reynolds, Dr. Bobby W. Sandage, Jr. and Dr. William D. Schwieterman, at the Annual Meeting for a term of one year to serve until the 2019 annual meeting of stockholders and until their respective successors have been elected and qualified.

Our Board of Directors has reviewed the materiality of any relationship that each of our directors has with the Company, either directly or indirectly. Based upon this review, our Board has determined that each of the nominees except for Dr. Chaplin and Dr. Schwieterman qualify as “independent directors” as defined under the rules of The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies.

Proxies received in connection with the Annual Meeting will be voted for no more than five director nominees. A plurality of the shares voted affirmatively at the Annual Meeting is required to elect each nominee as a director. We will vote your shares as you specify on your proxy card. If you sign, date and return the proxy card but do not specify how you want your shares voted, we will vote them FOR the election of the nominees listed below. If unforeseen circumstances (such as death or disability) make it necessary for the Board of Directors to substitute another person for any of the nominees, we will vote your shares FOR that other person. If we do not name a substitute nominee, the size of the Board of Directors will be reduced.

Set forth below are the names of the persons nominated as directors, their ages, their offices in the Company, if any, their principal occupations or employment for at least the past five years, the length of their tenure as directors and the names of other public companies in which such persons hold or have held directorships during at least the past five years. Additionally, information about the specific experience, qualifications, attributes or skills that led to our Board of Directors’ conclusion at the time of filing of this proxy statement that each person listed below should serve as a director is set forth below. Each nominee for election to the Board of Directors has consented to being named as a nominee and has agreed to serve if elected. If elected, each director would serve for aone-year term, expiring at the 2019 annual meeting of stockholders and until his successor is elected. Each nominee for election to the Board of Directors is currently serving as a director.

The following table sets forth certain information about each nominee. The ages of the nominees are as of March 30, 2018.

6David J. Chaplin, Ph.D.Dr. Chaplin has been a member of our Board of Directors since January 2013. Dr. Chaplin also served as our Chief Scientific Officer from May 2015 through January 2018, when he retired from his position as Chief Scientific Officer. Prior to serving as our Chief Scientific Officer, Dr. Chaplin was President and Chief Executive Officer from May 2014 until May 2015, and Head of Research and Development from 2000 until 2011. From 1999 to 2000, Dr. Chaplin served as Vice President of Oncology at Aventis Pharma in Paris, where he was in charge of drug development from preclinical through phase 1 trials. Prior to the merger of Rhone Poulenc Rorer (“RPR”) with Hoechst Marion Roussell, Dr. Chaplin was Senior Director of Oncology at

PROPOSAL 1: TO AUTHORIZE THE FILING OF AN AMENDMENT TO THE COMPANY’S RESTATED CERTIFICATE OF INCORPORATION TO EFFECT RPR from 1998 to 1999. From 1992 to 1998, Dr. Chaplin headed up the Cancer Research Campaign’s (“CRC”) Tumor Microcirculation Group, based at the Gray Laboratory Cancer Research Trust, Mount Vernon Hospital, London. During this time, he was also a member of the CRC Phase I/II clinical trials committee. Dr. Chaplin also served as Section Head of Cancer Biology at Xenova in the U.K. from 1990 to 1992, and held a senior staff appointment at the British Columbia Cancer Research Centre from 1982 to 1990. Dr. Chaplin has a B.Sc. in chemistry from the University of Essex, a M.Sc. in pharmacology from the University of Southampton, and completed his Ph.D. in tumor biology at the University of London. Since July 2012, Dr. Chaplin has been a director of PHusis Therapeutics, Inc., a privately held biopharmaceutical company in the United States developing inhibitors of proteins with regulatoryPH-domains that drive cancer growth. Since 2017, Dr. Chaplin has been a director of FasT Biopharma Ltd., a privately held company in the United Kingdom developing antibody based therapeutics. The Board believes that Dr. Chaplin’s expertise as one of the developers of the Company’s technology and his experience in the oncology field, together with his relationships with collaborators working on similar technology in this field, qualify Dr. Chaplin to serve as a director and led to the Board’s conclusion that he should be a member of the Board of Directors.

Simon C. Pedder, Ph.D. Dr. Pedder has been a member of our Board of Directors since March 2016. Dr. Pedder currently serves as the Vice President of Corporate Strategy and Business Development of Athenix, Inc., a private global specialty oncology pharmaceutical company. From April 2014 through June 2015, Dr. Pedder served as the President and Chief Executive Officer of Cellectar Biosciences, Inc., a biopharmaceutical company developing compounds for the treatment, diagnosis and imaging of cancer, and served as Cellectar’s Acting Chief Executive Officer from October 2013 until April 2014. Dr. Pedder also served as a member of the board of directors of Cellectar from October 2013 until June 2015. From May 2004 through July 2012, Dr. Pedder served as President, Chief Executive Officer and as a director of Chelsea Therapeutics, Inc., a public development stage biopharmaceutical company. Dr. Pedder has a Bachelor of Environmental Studies from the University of Waterloo, a Master of Science in Toxicology from Concordia University and a Ph.D. in Pharmacology from the Medical College at the University of Saskatchewan College of Medicine. Dr. Pedder currently serves on the board of directors of Cerecor, Inc., Eboo Pharmaceuticals, Inc., a private development-stage pharmaceutical company, and Atlantic Research Group, a private contract research organization. Dr. Pedder also served as a member of the board of directors of Cellectar from October 2013 until June 2015. The Board believes Dr. Pedder’s experience in cancer drug development and his experience managing public life sciences companies qualify Dr. Pedder to serve as a director of the Company and led to the Board’s conclusion that Dr. Pedder should be a member of the Board of Directors.

Donald R. Reynolds.Mr. Reynolds has been a member of our Board of Directors since October 2016. Mr. Reynolds is a practicing attorney and partner at the law firm of Wyrick Robbins Yates & Ponton LLP with experience in the areas of capital markets, securities law, mergers & acquisitions, venture capital and general corporate law. Mr. Reynolds also currently teaches Securities Regulation at Campbell University’s law school and guest lectures on corporate governance at the University of North Carolina Chapel Hill’s Kenan-Flagler Business School. Since Mr. Reynolds’s elevation to partner at the law firm of Wyrick Robbins Yates & Ponton LLP in 1996, he has participated in a variety of the firm’s internal committees, including the firm’s Executive Committee, Strategic Planning Committee, Nominating Committee and Compensation Committee. Mr. Reynolds received his B.A. from Whitman College and his J.D. from New York University School of Law. He is currently licensed to practice law in California and North Carolina. Mr. Reynolds currently serves as a member of the board of directors of Atlantic Research Group, Inc., a private clinical research organization, and as Chair of the board of directors of USA Taekwondo, thenon-profit national governing body for the sport. The Board believes that Mr. Reynolds’s extensive experience as a practicing capital markets attorney qualifies Mr. Reynolds to serve as a director of the Corporation and led to the Board’s conclusion that he should be a member of the Board.

Bobby W. Sandage, Jr., Ph.D. Dr. Sandage has been a member of our Board of Directors since October 2016. Dr. Sandage currently serves as the president and chief executive officer of Euclises Pharmaceuticals, Inc., a private drug discovery and development company advancingcyclooxygenase-2(COX-2) inhibitors for cancer therapy. Since August of 2016, he has served as a general partner of Cultivation Capital, a venture capital firm

specializing in investments in private technology and life sciences companies. Dr. Sandage is currently a member of the board of directors of Immunophotonics, Inc., a private cancer vaccine development company, EDIS Solutions, LLC, a private healthcare information technology company, and Euclises Pharmaceuticals, Inc. The Board believes that Dr. Sandage’s experience managing public life sciences companies and his extensive prior work on New Drug Applications, qualify Dr. Sandage to serve as a director of the Corporation and led to the Board’s conclusion that Dr. Sandage should be a member of the Board of Directors.

William D. Schwieterman, M.D.Since May 2015, Dr. Schwieterman has served as President and Chief Executive Officer of Mateon. Dr. Schwieterman has also been an independent consultant to biotech and pharmaceutical companies, including to Mateon, specializing in clinical development since July 2002. Dr. Schwieterman is a board-certified internist and a rheumatologist. Dr. Schwieterman was previously a part-time employee of Perceptive Advisors, LLC, a hedge fund based in New York, NY. From 2009 to 2014, Dr. Schwieterman was the Chief Medical Officer of Chelsea Therapeutics, Inc., a publicly traded biopharmaceutical development company, where he led the Chelsea Therapeutics clinical development team toward the approval of droxidopa for the treatment of symptoms of Parkinson’s disease and other neurogenerative diseases. Dr. Schwieterman was formerly Chief of the Medicine Branch and Chief of the Immunology and Infectious Disease Branch in the Division of Clinical Trials at the Food and Drug Administration (the “FDA”). In these capacities and others, Dr. Schwieterman spent 10 years at the FDA in the Center for Biologics overseeing a wide range of clinical development plans for a large number of different types of molecules. Dr. Schwieterman holds a B.S. and M.D. from the University of Cincinnati. Dr. Schwieterman does not currently serve, and has not served in the past five years, as a member of the board of directors of another reporting company or of any registered investment company. The Board believes that Dr. Schwieterman’s medical training and his expertise with regulatory matters involving the FDA and the clinical trials process are invaluable skills that Dr. Schwieterman brings to his Board service and led to the Board’s conclusion that Dr. Schwieterman should be a member of the Board of Directors.

A REVERSE STOCK SPLIT OF OUR COMMON STOCK, $0.01 PAR VALUE PER SHARE, AT A RATIO IN THE RANGE OF 1:2 TO 1:4, SUCH RATIO WITHIN THAT RANGE TO BE DETERMINED BY plurality of the shares voted for each nominee at the Annual Meeting is required to elect each nominee as a director.

THE BOARD OF DIRECTORS CONSISTENT WITHRECOMMENDS THE GUIDELINES DESCRIBEDELECTION TO THE BOARD OF DIRECTORS OF EACH DIRECTOR NOMINEE NAMED ABOVE, AND PROXIES SOLICITED BY THE BOARD WILL BE VOTED IN THIS PROXY STATEMENT, ANDFAVOR OF THE FILINGELECTION OF SUCH AMENDMENT TO BE IMPLEMENTED, IF AT ALL, NOT LATER THAN NOVEMBER 27, 2016NOMINEES UNLESS A STOCKHOLDER INDICATES OTHERWISE ON THE PROXY.

PROPOSAL 2: APPROVAL OF THE COMPANY’S AMENDED AND RESTATED 2015 EQUITY INCENTIVE PLAN.

General

Our Board of Directors has adopted and is recommendingrequesting that our stockholders approve an amendmentthe Company’s Amended and Restated 2015 Equity Incentive Plan as attached as Appendix A to our Charter,this proxy statement (the “Amended and thereby authorizeRestated 2015 Plan” or the “2015 Plan”). The Amended and Restated 2015 Plan was approved by our Board of Directors on April 18, 2018, effective upon approval by our stockholders at the Annual Meeting, and includes an increase in their discretion, to effect the Reverse Stock Split no later than November 27, 2016. Holders of our common stock, $0.01 par value per share, are being asked to approve the proposal that Article Fourth of the Charter be amended to effect the Reverse Split (such split to combine a number of outstandingauthorized shares under the 2015 Plan from 4,725,781 shares of our common stock between two (2)to an aggregate of 7,250,000 shares of our common stock. The number of shares currently authorized under our 2015 Plan includes 4,000,000 shares approved for the 2015 Plan and four (4), such number consisting725,781 shares that were approved for the 2015 Plan if they were not issued under the Mateon Therapeutics, Inc. 2005 Stock Plan (the “2005 Plan”).

The 2015 Plan was approved by our Board of only wholeDirectors and stockholders in 2015 and amended and restated by our Board of Directors in 2017.

As of April 30, 2018, options to purchase    shares into one (1) share of common stock). Pursuantstock are outstanding under the 2015 Plan, options to purchase    shares of common stock are outstanding under the law2005 Plan, no shares have been issued upon the exercise of options granted under the State2015 Plan, 83,295 shares have been issued upon the exercise of Delaware, our state of incorporation,options granted under the 2005 Plan and    options remain available for issuance under the 2015 Plan. By its terms, the 2015 Plan may be amended by the Board of Directors, must adopt thisprovided that any amendment which the Board of Directors determines requires stockholder approval is subject to receiving such stockholder approval.

This amendment is being submitted to you for approval at the Annual Meeting in order to ensure favorable federal income tax treatment for grants of incentive stock options under Section 422 of the Internal Revenue Code of 1986, as amended (the “Code”).

Generally, shares of common stock reserved for awards under the Amended and Restated 2015 Plan that lapse or are canceled will be added back to the share reserve available for future awards. However, shares of common stock tendered in payment for an award or shares of common stock withheld for taxes will not be available again for grant. The Amended and Restated 2015 Plan provides that no participant may receive awards for more than 500,000 shares of common stock in any fiscal year.

Our Board, the Compensation Committee and management all believe that the effective use of stock-based long-term incentive compensation is vital to our Charterability to attract qualified employees and submitdirectors that will be instrumental in the amendmentperformance of the Company in the future. The Plan will maintain and enhance the key policies and practices adopted by our management and Board of Directors to align employee and stockholder interests. Our future success depends, in large part, upon our ability to maintain a competitive position in attracting, retaining and motivating key personnel. We believe that the increase in the number of shares available for issuance under our 2015 Plan is essential to permit our management to continue to provide long-term, equity-based incentives to present and future key employees, consultants and directors. Accordingly, our Board of Directors believes approval of the Company’s Amended and Restated 2015 Equity Incentive Plan, including the proposed increase in the number of shares authorized to be granted thereunder, is in our best interests and those of our stockholders for their approval. and recommends a vote “FOR” the approval of the Amended and Restated 2015 Equity Incentive Plan.

The formfollowing is a brief summary of amendmentthe Amended and Restated 2015 Plan. This summary is qualified in its entirety by reference to our Charter to effect the Reverse Stock Splittext of the Amended and Restated 2015 Plan, a copy of which is attached as Appendix BA to this proxy statement.

Material Features of the Amended and Restated 2015 Plan.

Eligibility. The amendment will permitAmended and Restated 2015 Plan allows us, under the Boarddirection of Directorsour Compensation Committee, to effectmake grants of stock options, restricted and unrestricted stock awards, and other stock-based awards to employees, consultants and directors. The purpose of these awards is to attract and retain key individuals, further align employee and stockholder interests, and provide additional incentive for them to promote our success or the Reverse Stock Split at any timesuccess of our affiliates. The Amended and Restated 2015 Plan provides an essential component of the total compensation package, reflecting the importance that we place on or prior to November 27, 2016. The Boardaligning the interests of Directors may effect only one reverse stock split as a resultkey individuals with those of this authorization. The Board of Directors’ decision as to whetherour stockholders. All employees, directors, and when to effect the Reverse Stock Split will be based on a number of factors, including market conditions, existing and expected trading prices for our common stock, and the continued listing requirements of The NASDAQ Capital Market. Although our stockholders may approve the Reverse Stock Split, we will not effect the Reverse Stock Split if the Board of Directors does not deem it to be in the best interestsconsultants of the Company and its stockholders. The Reverse Stock Split, if authorized pursuantaffiliates are eligible to this resolution and if determined by the Board of Directors, in their discretion, to beparticipate in the best interests of the CompanyAmended and its stockholders, will be effected, if at all, on or prior to November 27, 2016.

In determining whether to implement the Reverse Stock Split, the Board of Directors has determined that it will not implement the Reverse Stock Split if, at the time of the Board’s consideration, the Company has already regained compliance with the minimum closing bid price requirement of the NASDAQ Capital Market under NASDAQ Listing Rule 5550(a)(2). In addition, as guidelines to determine the reverse split ratio to be implemented if the proposal is approved, the Board of Directors will target a stock trading price of $2.00 to $3.00 per share immediately following the reverse split. For example, if the common stock is trading at $0.80 per share immediately before the decision to implement the Reverse Stock Split, the Board of Directors would implement the reverse split at a ratio of 1-for-3, which would result in a trading price immediately following the reverse split of $2.40 per share (pre-split trading price of $0.80 times the reverse split ratio of three (3)).

The proposed amendment to our Charter to effect the Reverse Stock Split will not change the number of authorized shares of common stock or preferred stock, or the par value of common stock or preferred stock.Restated 2015 Plan. As of the date of this proxy statement, we have no definitive, specific plans, arrangements or understandings relatingApril 30, 2018, there were approximately    individuals eligible to the issuance of a material amount of additional shares of authorized common stock that will become available following the reverse stock split in the near term.

Purpose and Background of the Reverse Stock Split

participate. On December 1, 2015, we received a deficiency letter from The NASDAQ Stock Market LLC indicating that, for the lastApril 30, consecutive business days ended November 30, 2015, the bid price for our common stock had closed below the minimum $1.00 per share required for continued inclusion on The NASDAQ Capital Market under NASDAQ Listing Rule 5550(a)(2). Pursuant to NASDAQ Listing Rule 5810(c)(3)(A), we were afforded 180 calendar days, or until May 31, 2016, to regain compliance with the

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minimum bid price requirement. On June 1, 2016, we were provided an additional 180-day compliance period by demonstrating that the Company met the applicable market value of publicly held shares requirement for continued listing and all other applicable standards for initial listing on The NASDAQ Capital Market (except the bid price requirement), and by providing written notice of our intention to cure the minimum bid price deficiency during this second grace period, including a cure through the implementation of a reverse stock split. If the Company fails to regain compliance during the second grace period, or by November 27, 2016, the Company’s stock will be subject to delisting by NASDAQ. Our common stock will continue to be listed on The NASDAQ Capital Market during this second grace period.

On August 16, 2016, the Board of Directors approved the proposal authorizing the Reverse Stock Split because the Board of Directors believes that effecting the Reverse Stock Split could be an effective means of regaining compliance with the bid price requirement for continued listing of our common stock on The NASDAQ Capital Market.

NASDAQ Requirements for Continued Listing

Our common stock is quoted on The NASDAQ Capital Market under the symbol “MATN.” One of the requirements for continued listing on the NASDAQ Capital Market is maintenance of a minimum closing bid price of $1.00 per share. On September 15, 2016,2018, the closing market price per share of our common stock was $[●]$    , as reported by The NASDAQ Capital Market. On December 1,on OTCQX marketplace.

Stock Options. Stock options granted under the Amended and Restated 2015 we received a deficiency letter from The NASDAQ Stock Market LLC indicating that the bid price for our commonPlan may either be incentive stock had closed below the minimum $1.00 per share required for continued inclusion on The NASDAQ Capital Market as noted above.

We cannot be sure that our stock price will comply withoptions (“ISOs”), which are intended to satisfy the requirements for continued listingof Section 422 of the Code, ornon-qualified stock options, which are not intended to meet those requirements. ISOs may only be granted to employees of the Company and its affiliates.Non-qualified options may be granted to employees, directors and consultants of the Company and its affiliates. The exercise price of a stock option may not be less than 100% of the fair market value of our common stock on The NASDAQ Capital Marketthe date of grant. If an ISO is granted to an individual who owns more than 10% of the combined voting power of all classes of our capital stock, the exercise price may not be less than 110% of the fair market value of our common stock on the date of grant and the term of the ISO may not be longer than five years. Options may not have a term longer than ten years, except that if an ISO is granted to an individual who owns more than 10% of the combined voting power of all classes of our capital stock, it may not have a term longer than five years from the date of the grant unless otherwise provided in the future,option agreement.

Award agreements for stock options include rules for exercise of the stock options after termination of service. Options may not be exercised unless they are vested, and no option may be exercised after the end of the term set forth in the award agreement. Generally, stock options will be exercisable for three months after termination of service for any reason other than death or total and permanent disability, and for twelve months after termination of service on account of death or total and permanent disability.

Restricted Stock. Restricted stock is common stock that we will complyis subject to restrictions, including a prohibition against transfer and a substantial risk of forfeiture, until the end of a “restricted period” during which the grantee must satisfy certain vesting conditions. If the grantee does not satisfy the vesting conditions by the end of the restricted period, the restricted stock is forfeited.

During the restricted period, the holder of restricted stock has the rights and privileges of a regular stockholder, except that the restrictions set forth in the applicable award agreement apply. For example, the holder of restricted stock may vote and receive dividends on the restricted shares; but he or she may not sell the shares until the restrictions are lifted.

Other Stock-Based Awards. The Amended and Restated 2015 Plan also authorizes the grant of other types of stock-based compensation including, but not limited to stock appreciation rights, phantom stock awards, and stock unit awards. Our Compensation Committee may award such stock-based awards subject to such conditions and restrictions as it may determine. These conditions and restrictions may include continued employment with us through a specified restricted period.

Plan Administration. In accordance with the terms of the Amended and Restated 2015 Plan, our Board of Directors has authorized our Compensation Committee to administer the Amended and Restated 2015 Plan. The Compensation Committee may delegate part of its authority and powers under the Amended and Restated 2015 Plan to one or more of our directors and/or officers, but only our Board of Directors or our Compensation

Committee can make awards to participants who are directors or executive officers of the Company. In accordance with the provisions of the Amended and Restated 2015 Plan, our Compensation Committee determines the terms of awards, including:

In addition, our Compensation Committee may, in its discretion, amend any term or condition of any outstanding award, other than reducing the exercise price or purchase price, provided that (i) the term or condition as amended is not prohibited by the Amended and Restated 2015 Plan; (ii) any amendment does not impair the rights of a participant under any award previously granted without that participant’s consent; and (iii) any amendment will be made only after the Compensation Committee determines whether the amendment would cause any adverse tax consequences to the participant.

Stock Dividends and Stock Splits. If our common stock loses its status on The NASDAQ Capital Market, our common stock would likely trade in the over-the-counter market.

If our shares were to trade on the over-the-counter market, selling your stock could become more difficult and more expensive becauseshall be subdivided or combined into a greater or smaller quantitiesnumber of shares would likely be bought and sold, and transactions could be delayed. In addition, in the event our common stock is delisted, broker-dealers have certain regulatory burdens imposed upon them, which may discourage broker-dealers from effecting transactions in our common shares, further limiting the liquidity of our common shares. Also, some broker-dealers may be required to sell shares of our common stock prior to or shortly after the delisting, creating a potential imbalance of shares in the market. Any one or all of these factors could result in lower prices and larger spreads in the bid and ask prices for common shares.

Such delisting from The NASDAQ Capital Market and continued or further declines in our share price could also greatly impair our ability to raise additional necessary capital through equity or debt financing. In addition, if we were to seek additional capital through an equity financing, such delisting from The NASDAQ Capital Market would be very likely to have a significant and detrimental impact on the terms of an equity financing because:

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In light of the factors mentioned above, our Board of Directors unanimously approved this proposal as a potential means of increasing the bid price of our common stock to above $1.00 per share in compliance with The NASDAQ Stock Market requirements.

There are risks associated with the Reverse Stock Split, including that the Reverse Stock Split may not result in a sustained increase in the per share price of our common stock. We cannot predict whether the Reverse Stock Split will increase the market price for our common stock on a sustained basis. The history of similar stock split combinations for companies in like circumstances is varied. There is no assurance that the market price per share of our common stock after the Reverse Stock Split will rise in proportion to the reduction individend, the number of shares of our common stock outstanding beforedeliverable upon exercise of an option issued or upon issuance of an award shall be appropriately increased or decreased proportionately, and appropriate adjustments shall be made in the Reverse Stock Split and the marketpurchase price per share will either exceedto reflect such subdivision, combination, or remainstock dividend.

Corporate Transactions. Upon a merger or other reorganization event, the Compensation Committee or the successor board, may, in excessits sole discretion, take any one or more of the $1.00 minimum bid pricefollowing actions pursuant to the Amended and Restated 2015 Plan, as requiredto some or all outstanding awards:

The market price

Amendment and Termination.The Company expects thatAmended and Restated 2015 Plan may be amended by our transfer agent will act as exchange agent for purposes of implementing the exchange of stock certificates. Holders of pre-split shares willstockholders. It may also be asked to surrender to the exchange agent certificates representing pre-split shares in exchange for certificates representing post-split shares in accordance with the procedures to be set forth in a letter of transmittal to be sentamended by the CompanyCompensation Committee, provided that any amendment approved by the Compensation Committee which is of a scope that requires stockholder approval as required by the rules of order to ensure favorable federal income tax treatment for any incentive stock options under Code Section 422, or its exchange agent. No new certificates will be issuedfor any other reason is subject to a stockholder untilobtaining such stockholder has surrenderedapproval. However, no such stockholder’saction may adversely affect any rights under any outstanding certificate(s) together with the properly completed and executed letter of transmittal to the exchange agent. Any pre-split shares submitted for transfer, whether pursuant to a sale or other disposition, or otherwise, will automatically be exchanged for post-split shares.

Some stockholders hold their shares of common stock in certificate form or a combination of certificate and book-entry form. We expect that our transfer agent will act as exchange agent for purposes of implementing the exchange of stock certificates, if applicable. If you are a stockholder holding pre-split shares in certificate form, you will receive a transmittal letter from the Company’s transfer agent as soon as practicable after the effective time of the Reverse Stock Split. The transmittal letter will be accompanied by instructions specifying how you can exchange your certificate representing the pre-split shares of our common stock for a statement of holding, together with any payment of cash in lieu of fractional shares to which you are entitled. When you submit your certificate representing the pre-split shares of our common stock, your post-split shares of our common stock will be held electronically in book-entry form. This means that, instead of receiving a new stock certificate, you will receive a statement of holding that indicates the number of post-split shares you own in book-entry form. We will no longer issue physical stock certificates unless you make a specific request for a share certificate representing your post-split ownership interest.

STOCKHOLDERS SHOULD NOT DESTROY ANY STOCK CERTIFICATE(S) AND SHOULD NOT SUBMIT ANY CERTIFICATE(S) UNTIL REQUESTED TO DO SO.

Beginning on the effective time of the Reverse Stock Split, each certificate representing pre-split shares will be deemed for all corporate purposes to evidence ownership of post-split shares.

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Fractional Shares

No fractional shares will be issued in connection with the Reverse Stock Split. Stockholders of record who otherwise would be entitled to receive fractional shares because they hold a number of pre-split shares not evenly divisible by the number of pre-split shares for which each post-split share is to be exchanged, will be entitled, upon surrender to the exchange agent of certificates representing such shares, to a cash payment in lieu thereof at a price equal to the fraction to which the stockholder would otherwise be entitled multiplied by the closing price of the common stock, as reported by NASDAQ, on the last trading day prior to the effective date of the split (or if such price is not available, the price determined by the Board of Directors). The ownership of a fractional interest will not give the holder thereof any voting, dividend, or other rights except to receive payment therefor as described herein.

Stockholders should be aware that, under the escheat laws of the various jurisdictions where stockholders reside, where the Company is domiciled, and where the funds will be deposited, sums due for fractional interests that are not timely claimed after the effective date of the Reverse Stock Split may be required to be paid to the designated agent for each such jurisdiction, unless correspondence has been received by the Company or the exchange agent concerning ownership of such funds within the time permitted in such jurisdiction. Thereafter, stockholders otherwise entitled to receive such funds will have to seek to obtain them directly from the state to which they were paid. Each holder should seek advice based onaward without the holder’s particular circumstances from an independent tax advisor.consent.

Effect on Stock Plans

AsDuration of September 15, 2016, options to purchase 4,049,415 shares of common stock are outstanding under the Company’s two equity incentive plans, the 2015 Equity Incentive Plan (the “2015 Plan”)Plan. The Amended and the 2005 Stock Plan, and 676,366 options remain available for issuance under the 2015 Plan. If the Reverse Stock Split is approved by our stockholders and our Board of Directors decides to implement the Reverse Stock Split, as of the effective date, the number of all outstanding equity awards, the number of shares available for issuance and the exercise price, grant price or purchase price, as applicable, relating to any award under our stock plans, will be proportionately adjusted using the reverse stock split ratio selected by our Board of Directors (subject to the treatment of fractional shares to be determined by our Board of Directors). Our Board of Directors has also authorized the Company to effect any other changes necessary, desirable or appropriate to give effect to the Reverse Stock Split, including any applicable technical, conforming changes. For example, if a 1-for-2 reverse stock split is effected, the 676,366 shares that remain available for issuance under theRestated 2015 Plan as of September 15, 2016, would be adjusted to equal approximately 338,183 shares. In addition, the exercise price per share of each outstanding stock option would be increasedwill expire by a factor of 2 and the number of shares subject to each outstanding stock option would be reduced by 1/2. Following these changes, the aggregate exercise price payable by the optionee to the Company would remain the same and the percentage of the Company that the optionee purchased would remain the same, but the price per share would increase and the number of shares acquired would decrease.its terms on February 26, 2025.

Accounting Matters

The Reverse Stock Split will not affect the stockholders’ equity accounts on our balance sheet. However, because the par value of our common stock will remain unchanged on the effective date of the split, the components that make up the common stock capital account and the additional paid-in capital account will change by offsetting amounts. Depending on the size of the reverse stock split the Board of Directors implements, the stated capital component will be reduced to an amount between one-half (1/2) and one-fourth (1/4) of its present amount, and the additional paid-in capital component will be increased by the amount which the stated capital is reduced. The per share net loss and net book value of our common stock will be increased because there will be fewer shares of common stock outstanding. All per share amounts for all periods for which we present financial statements will be restated to reflect the Reverse Stock Split.

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No Dissenters’ Rights

Under the Delaware General Corporation Law, the Company’s stockholders will not be entitled to dissenters’ rights with respect to the Reverse Stock Split, and we do not intend to independently provide stockholders with any such right.

Material United States Federal Income Tax Consequences of the Reverse Stock Split

Each holder of common stock is hereby notified that any discussion of U.S. Federal tax issues in this proxy statement has been included by the Company in furtherance of the Reverse Stock Split on the terms described herein, and each such holder should seek advice based on his, her, or its particular circumstances from an independent tax advisor.

Considerations.The following discussion describes the anticipated material United States Federalfederal income tax consequences to “U.S. holders” (as defined below) of Company capital stock relating to the Reverse Stock Split. This discussion is based upon the Internal Revenue Code of 1986, as amended (the “Code”), Treasury Regulations, judicial authorities, published positions of the Internal Revenue Service (“IRS”), and other applicable authorities, all as currently in effect and all of which are subject to change or differing interpretations (possibly with retroactive effect). We have not obtained a ruling from the IRS or an opinion of legal or tax counsel with respect to the tax consequences of the Reverse Stock Split. The following discussion is for information purposes onlyissuance and is not intended as tax or legal advice. Each holder should seek adviceexercise of stock options and other awards under the Amended and Restated 2015 Plan, based on the holder’s particular circumstancescurrent provisions of the Code and regulations, are as follows. Changes to these laws could alter the tax consequences described below. This summary assumes that all awards granted under the Amended and Restated 2015 Plan are exempt from an independent tax advisor.

For purposesor comply with, the rules under Section 409A of this discussion, the term “U.S. holder” means a beneficial owner of Company capital stock that is for United States Federal income tax purposes:Code related to nonqualified deferred compensation.

This discussion assumes that a U.S. holder holds Company capital stockNew Plan Benefits. The amounts of any future grants under the Amended and Restated 2015 Plan are not determinable as a capital asset withinawards under the meaning of Code Section 1221. This discussion does not address allAmended and Restated 2015 Plan and will be granted at the sole discretion of the tax consequences that may be relevant to a particular Company stockholder or to Company stockholders that are subject to special treatment under United States Federal income tax laws including, but not limited to, financial institutions, tax-exempt organizations, insurance companies, regulated investment companies, persons that are broker-dealers, traders in securities who elect the mark-to-market method of accounting for their securities, or Company stockholders holding their shares of Company capital stock as part of a “straddle,” “hedge,” “conversion transaction,”Compensation Committee, or other integrated transaction. This discussion also does not addressdelegated persons and we cannot determine at this time either the tax consequences topersons who will receive awards under the Company,Amended and Restated 2015 Plan or to Company stockholders that own 5% or more of the Company’s capital stock, are affiliates of Company, or are not U.S. holders. In addition, this discussion does not address other United States Federal taxes (such as gift or estate taxes or alternative minimum taxes), the tax consequences of the Reverse Stock Split under state, local, or foreign tax laws or certain tax reporting requirements that may be applicable with respect to the reverse stock split. No assurance can be given that the IRS would not assert, or that a court would not sustain, a position contrary to any of the tax consequences set forth below.

If a partnership (or other entity treated as a partnership for United States Federal income tax purposes) is a Company stockholder, the tax treatment of a partner in the partnership (or any equity owner of such other entity) will generally depend upon the status of the person and the activities of the partnership or other entity treated as a partnership for United States Federal income tax purposes.

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Tax Consequences of the Reverse Stock Split Generally

We believe that the Reverse Stock Split will qualify as a “reorganization” under Section 368(a)(1)(E) of the Code. Accordingly, provided that the fair market value of the post-Reverse Stock Split shares is equal to the fair market value of the pre-Reverse Stock Split shares surrendered in the Reverse Stock Split:

Cash Received Instead of a Fractional Share

A U.S. holder who receives cash instead of a fractional share of post-Reverse Stock Split shares will be treated as having received the fractional share of post-Reverse Stock Split shares pursuant to the Reverse Stock Split and then as having exchanged the fractional share of post-Reverse Stock Split shares for cash in a redemption by the Company. In general, this deemed redemption will be treated as a sale or exchange, provided the redemption is not essentially equivalent to a dividend as discussed below. Gain or loss generally will be recognized based on the difference between the amount of cash received and the portion of the U.S. holder’s adjusted tax basis of the pre-Reverse Stock Split shares exchanged in the Reverse Stock Split which is allocable to such fractional share. Such gain or loss generally will be long-term capital gain or loss if the U.S. holder’s holding period for such pre-Reverse Stock Split shares is more than one year as of the effective date of the Reverse Stock Split, and otherwise will be short-term capital gain or loss.

The receipt of cash is “not essentially equivalent to a dividend” if the reduction in a U.S. holder’s proportionate interest in Company resulting from the Reverse Stock Split (taking into account for this purpose shares of common stock which such holder is considered to own under certain attribution rules) is considered a “meaningful reduction” given such U.S. holder’s particular facts and circumstances. The IRS has ruled that a small reduction by a minority stockholder whose relative stock interest is minimal and who exercises no control over the affairs of a corporation can satisfy this test. If the receipt of cash in lieu of a fractional share is not treated as capital gain or loss under the test just described, it will be treated first as ordinary dividend income to the extent of a U.S. holder’s ratable share of Company’s current and accumulated earnings and profits, then as a tax-free return of capital to the extent of the portion of the U.S. holder’s adjusted tax basis of the pre-Reverse Stock Split shares which is allocable to such fractional share, and any remaining amount will be treated as capital gain.

Information Reporting and Backup Withholding

Cash payments received by a U.S. holder of Company capital stock pursuant to the Reverse Stock Split are subject to information reporting, and may be subject to backup withholding at the applicable rate specified by the U.S. Internal Revenue Service (currently 28%) if the holder fails to provide a valid taxpayer identification number and comply with certain certification procedures or otherwise establish an exemption from backup withholding. Backup withholding is not an additional United States Federal income tax. Rather, the U.S. Federal income tax liability of the person subject to backup withholding will be reduced by the amount of the tax withheld. If backup withholding results in an overpayment of taxes, a refund may be obtained provided that the required information is timely furnished to the IRS.

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Reservation of Right to Abandon Reverse Stock Split

We reserve the right to not file the certificate of amendment and to abandon any reverse stock split without further action by our stockholders at any time before the effectiveness of the filing with the Secretary of the State of Delaware of the certificate of amendment, even if the authority to effect this amendment is approved by our stockholders at the Special Meeting. By voting in favor of a reverse stock split, you are expressly also authorizing the Board to delay, not proceed with, and abandon, this proposed amendment if it should so decide, in its discretion, that such action is in the best interests of our stockholders.awards.

Vote Required and Board of Directors’ Recommendation

ApprovalFor these reasons, the Board of Directors has recommended approval of the Amended and Restated 2015 Plan which includes an increase in the number of shares authorized to be granted thereunder. The affirmative vote of a majority of the shares cast affirmatively or negatively at the Annual Meeting is required to approve the Amended and Restated 2015 Plan.

THE BOARD OF DIRECTORS RECOMMENDS APPROVAL OF THE AMENDED AND RESTATED 2015 EQUITY INCENTIVE PLAN, WHICH INCLUDES AN INCREASE IN THE NUMBER OF AUTHORIZED SHARES AVAILABLE FOR THE GRANT OF AWARDS UNDER THE 2015 PLAN FROM 4,725,781 SHARES TO 7,250,000 SHARES OF COMMON STOCK. PROXIES SOLICITED BY THE BOARD WILL BE VOTED IN FAVOR OF THE AMENDED AND RESTATED 2015 EQUITY INCENTIVE PLAN UNLESS A STOCKHOLDER HAS INDICATED OTHERWISE ON THE PROXY.

PROPOSAL 3: AMENDMENT OF OUR RESTATED CERTIFICATE OF INCORPORATION TO INCREASE FROM 70,000,000 SHARES TO 150,000,000 SHARES THE AGGREGATE NUMBER OF SHARES OF COMMON STOCK AUTHORIZED TO BE ISSUED

The Board of Directors has determined that it is advisable to increase our authorized common stock from 70,000,000 shares to 150,000,000 shares, and has voted to recommend that the stockholders adopt an amendment to our CharterRestated Certificate of Incorporation effecting the proposed increase. The full text of the proposed amendment to the Restated Certificate of Incorporation is attached to this proxy statement as Appendix B.

As of April 30, 2018,    shares of our common stock were issued and outstanding and an additional    shares were reserved for issuance upon the exercise of options granted under our various stock-based incentive plans. In addition, shares were reserved for issuance upon the exercise of warrants, excluding 7,312,500 shares to be reserved for the Series B Warrants (described below). Accordingly, a total of    shares of common stock are available for future issuance, prior to the consideration of shares required for the Series B Warrants.

Purpose, Background and Potential Effects of the Share Increase

The Company is in the business of developing investigational drugs for the treatment of cancer. We have financed our operations primarily through public offerings and private placements of our common stock. We do not currently have any commitments for future external funding, including any arrangements with larger pharmaceutical companies or others to pay for ouron-going development costs, and none of our product candidates have been approved for sale. The Company has very limited capital, with only $0.2 million in cash and cash equivalents as of March 31, 2018, and limited access to new sources of capital. We have no source of revenue and do not expect to receive any product revenue in the near future. Until we can generate a revenue from the sale of our product candidates or from corporate collaboration or licensing arrangements, which we may never do, we expect to finance future cash needs through public or private equity offerings, debt or other financings. Additionally, collaboration and licensing arrangements, often involve an equity investment. With the current small pool of authorized and unissued shares of common stock, Management believes that it is at a higher risk of being unable to raise additional capital if the Company’s stockholders do not approve the authorization of additional shares of common stock. In addition, if additional shares of common stock are not authorized, the Company may be more likely to issue shares of Preferred Stock that could be detrimental to the rights of common stockholders.

Management believes that the availability of additional authorized shares of common stock for issuance from time to time in the Board of Directors’ discretion in connection with possible future financings, collaboration and licensing arrangements, or for other corporate purposes, is desirable for all stockholders because it increases the number of potential alternatives available for the Company to operate its business and will provide the additional flexibility necessary to pursue its strategic objectives.

In addition, on April 12, 2018, we entered into subscription agreements with accredited investors for the sale of 14,625,000 shares of common stock and warrants to purchase 14,625,000 shares of common stock. The common stock was sold for a purchase price of $0.20 per share and the warrants are exercisable at $0.40 per share. Half of the warrants issued, for the purchase of an aggregate of 7,312,500 shares of common stock, were Series B Warrants (the “Series B Warrants”). The Series B Warrants will become exercisable following stockholder approval of an amendment to the Company’s Restated Certificate of Incorporation to increase the number of authorized shares of the Company’s common stock in an amount sufficient for the full exercise of the Series B Warrants (the “Stock Authorization”) and for two years thereafter. If the Stock Authorization is not obtained by June 30, 2018, the Series B Warrants will be exercisable for an additional two years. Pursuant to the terms of the subscription agreements relating to the financing described above, we are required to seek and obtain shareholder approval to amend and restate our certificate of incorporation to ensure the availability of sufficient

additional authorized but unissued shares of common stock for the full exercise of the Series B Warrants. The Board of Directors believes it is in our stockholders’ best interest to avoid the extension of the exercise period for the Series B Warrants by obtaining the Stock Authorization and amending our restated certificate prior to the June 30, 2018 deadline.

Other than the potential issuance of up to 7,312,500 shares of our common stock in connection with the exercise of the Series B Warrants, we currently have no definitive understandings, arrangements or agreements with respect to any future transactions or financings that would require us to authorize or issue new shares of our common stock.

The Board of Directors believes that the currently available authorized and unissued shares of common stock, in addition to being insufficient to allow for the exercise of all outstanding warrants, does not provide sufficient flexibility for corporate action in the future. Although we plan to continue to pursue sources of funding which do not involve the issuance of new equity securities, such as corporate collaborations and partnerships, if we are not successful with these efforts or if our Board of Directors otherwise determines that a financing through issuing additional shares is attractive, we want to be in a position to be able to complete such a transaction.

If this Proposal 3 is not approved by our stockholders, it is possible that financing alternatives for the Company may be limited by the lack of sufficient unissued and unreserved authorized shares of common stock, and stockholder value may be harmed by this limitation. In addition, our success depends in part on our continued ability to attract, retain and motivate highly qualified management and clinical and scientific personnel, and if this Proposal 3 is not approved by our stockholders, the lack of sufficient unissued and unreserved authorized shares of common stock to provide future equity incentive opportunities could adversely impact our ability to achieve these goals.

The issuance of additional shares of common stock could have the effect of diluting existing stockholder earnings per share, book value per share and voting power. Except for the Reverse Stock Split requires anexercise of the Series B Warrants, our stockholders do not have any right to purchase or subscribe for any part of any new or additional issuance of our securities.

Vote Required and Board of Directors’ Recommendation

The affirmative vote of a majority of the common stock outstanding and entitled to vote at the Special Meeting. Abstentions and broker non-votes will be counted towardsAnnual Meeting is required to approve the vote total for this proposal and will have the same effect as “against” votes.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” THE PROPOSAL TO AUTHORIZE THE FILING OF AN AMENDMENT TO THE COMPANY’S RESTATED CERTIFICATE OF INCORPORATION TO EFFECT A REVERSE STOCK SPLIT OF OUR COMMON STOCK, $0.01 PAR VALUE PER SHARE, AT A RATIO IN THE RANGE OF 1:2 TO 1:4, SUCH RATIO WITHIN THAT RANGE TO BE DETERMINED BY THE BOARD OF DIRECTORS CONSISTENT WITH THE GUIDELINES DESCRIBED IN THIS PROXY STATEMENT, AND THE FILING OF SUCH AMENDMENT TO BE IMPLEMENTED, IF AT ALL, NOT LATER THAN NOVEMBER 27, 2016.

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PROPOSAL 2: THE ADJOURNMENT OF THE SPECIAL MEETING

Our stockholders are being asked to consider and vote upon an adjournment of the Special Meeting, if necessary, if a quorum is present, to solicit additional proxies if there are not sufficient votes in favor of approval of a proposed amendment to our restated certificateRestated Certificate of incorporationIncorporation to effectuate a reverse stock split as describedeffect the proposed increase in Proposal 1.

Approval of the adjournment of the Special Meeting requires an affirmative vote of a majority of the votes properly cast for or against this proposal at the Special Meeting. Abstentions and broker non-votes (to the extent a broker does not exercise its authority to vote) will not be counted towards, and will have no effect on, the vote total for this proposal.our authorized shares.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE TO APPROVE THE ADJOURNMENTAMENDMENT TO OUR RESTATED CERTIFICATE OF INCORPORATION, AND PROXIES SOLICITED BY THE BOARD WILL BE VOTED IN FAVOR OF THE SPECIAL MEETING, IFAMENDMENT UNLESS A QUORUM IS PRESENT,STOCKHOLDER INDICATES OTHERWISE ON THE PROXY.

PROPOSAL 4: RATIFICATION OF APPOINTMENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

The Audit Committee has appointed OUM & Co. LLP (“OUM”), as our independent registered public accounting firm, to audit our financial statements for the year ending December 31, 2018. The Board proposes that the stockholders ratify this appointment. OUM audited our financial statements for the year ended December 31, 2017. We expect that representatives of OUM will be present at the annual meeting, will be able to make a statement if they so desire, and will be available to respond to appropriate questions.

In deciding to appoint OUM, the Audit Committee reviewed auditor independence issues with OUM and concluded that OUM has no commercial relationship with the Company that would impair its independence for the year ending December 31, 2018.

The submission of this matter to our stockholders at the Annual Meeting is not required by law or by ourBy-laws. The Board of Directors is nevertheless submitting it to the stockholders to ascertain their view. If this proposal is not approved at the Annual Meeting by the stockholders, the Audit Committee intends to reconsider, but might not change, its appointment of OUM & Co. LLP as the Company’s independent registered public accounting firm.

Audit Fees

The following table presents fees for professional audit services rendered by our independent public accounting firm, OUM & Co., LLP, for the audit of the Company’s annual financial statements for the years ended December 31, 2017 and December 31, 2016, and fees billed for other services rendered during those periods.

Prior to engagement, the Audit Committeepre-approves these services by category of service. The fees are budgeted, and the Audit Committee requires the independent registered public accounting firm and management to report actual fees versus the budget periodically throughout the year by category of service. During the year, circumstances may arise when it may become necessary to engage the independent registered public accounting firm for additional services not contemplated in the originalpre-approval. In those instances, the Audit Committee requires specificpre-approval before engaging the independent registered public accounting firm.

The Audit Committee may delegatepre-approval authority to one or more of its members. The member to whom such authority is delegated must report, for informational purposes only, anypre-approval decisions to the Audit Committee at its next scheduled meeting.

Vote Required and Board of Directors’ Recommendation

Approval of the ratification of appointment of our independent registered public accounting firm requires an affirmative vote of a majority of the votes cast on the proposal at the Annual Meeting.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE TO SOLICIT ADDITIONAL PROXIES IF THERE ARE NOT SUFFICIENT VOTES TO APPROVE PROPOSAL 1,RATIFY THE APPOINTMENT OF OUR INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM, AND PROXIES SOLICITED BY THE BOARD OF DIRECTORS WILL BE VOTED IN FAVOR OF THE ADJOURNMENTRATIFICATION UNLESS A STOCKHOLDER HAS INDICATEDINDICATES OTHERWISE ON THE PROXY.

MANAGEMENT AND CORPORATE GOVERNANCE

The Board of Directors

Our Board of Directors currently consists of five members: Dr. David J. Chaplin, Dr. Simon C. Pedder, Mr. Donald R. Reynolds, Dr. Bobby W. Sandage, Jr. and Dr. William D. Schwieterman. Under ourBy-laws, the number of members of our Board of Directors is fixed from time to time by the Board of Directors, and directors serve in office until the next annual meeting of stockholders and until their successors have been elected and qualified.

Committees of the Board and Meetings

Meeting Attendance. During the year ended December 31, 2017, the Board of Directors held eight meetings, and the various committees of the Board met a total of six times. The Board of Directors has established three committees whose functions and current members are noted below. The Audit Committee, the Compensation Committee, and the Nominating and Governance Committee (collectively, the “Board Committees”) are committees of the Board of Directors and consist solely of members of the Board of Directors. Each director who served during 2017 attended 75% or more of the aggregate number of meetings of the Board of Directors and Board Committees on which he served during 2017. The Board has also adopted a policy under which each member of the Board who chooses to attend the annual meeting of our stockholders is expected to do so at his or her own expense. One director in office at the time of our annual meeting of stockholders in 2017 standing forre-election attended our 2017 annual meeting.

Audit Committee. The Audit Committee consists of Dr. Sandage (Chairman), Dr. Pedder and Mr. Reynolds. During 2017, the Audit Committee held four meetings. Our Audit Committee has the authority to retain and terminate the services of our independent registered public accounting firm, reviews our annual financial statements, considers matters relating to accounting policy and internal controls, and reviews the scope of our annual audits. The Board has determined that Dr. Sandage is an “audit committee financial expert,” as the SEC has defined that term in Item 407 of RegulationS-K. The Board of Directors has adopted a charter for the Audit Committee, which is reviewed and reassessed annually by the Audit Committee. A copy of the Audit Committee’s written charter is publicly available on our website at www.mateon.com. All members of our Audit Committee qualify as independent under the definition promulgated by The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies.

Compensation Committee. The Compensation Committee consists of Dr. Pedder (Chairperson), Mr. Reynolds and Dr. Sandage. During 2017, the Compensation Committee held one meeting. The Compensation Committee’s roles and responsibilities include making recommendations to the Board of Directors regarding the compensation philosophy and compensation guidelines for our executives, the role and performance of our executive officers, and appropriate compensation levels for our CEO, which are determined without the CEO present, and other executives based on a comparative review of compensation practices of similarly situated businesses. The Compensation Committee also makes recommendations to the Board regarding the design and implementation of our compensation plans and the establishment of criteria and the approval of performance results relative to our incentive plans. Our Compensation Committee also administers our 2015 Plan and the Mateon Therapeutics, Inc. 2017 Equity Incentive Plan (the “2017 Plan”). Each member of the Compensation Committee qualifies as independent under the definition promulgated by The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies, and qualifies as a“Non-Employee Director” within the meaning of Rule16b-3 under the Exchange Act.

The Compensation Committee reviews and assesses the three main components of each named executive officer’s compensation: base salary, incentive compensation, and equity compensation. Adjustments to base salary are generally only made when there has been a change in the scope of the responsibilities of the named executive officer or when, based on a review of the base salary component of executive officers in companies of a similar size

and stage of development, the Compensation Committee members believe that an adjustment is warranted in order to remain competitive. The executive management of the Company determines and agrees with the Compensation Committee on its corporate goals and objectives for the ensuing year. At the end of each year, the attainment of each objective is assessed and incentive awards may be made to each executive based on his or her contribution to achieving the objectives. Awards are made based on either provisions of an executive’s employment agreement, or an assessment of each executive’s equity compensation position relative to the Company’s other executives.

The Compensation Committee also typically reviews our director compensation on at least an annual basis.

The Compensation Committee has the authority to directly retain the services of independent consultants and other experts to assist in fulfilling its responsibilities, although did not retain the services of any independent consultants in 2017.

A copy of the Compensation Committee’s written charter is publicly available on our website at www.mateon.com.

Nominating and Governance Committee. During 2017, the Nominating and Governance Committee held one meeting. The Nominating and Governance Committee consists of Mr. Reynolds (Chairman), Dr. Pedder and Dr. Sandage. The Nominating and Governance Committee’s role and responsibilities include making recommendations to the full Board as to the size and composition of the Board and making recommendations as to particular nominees to the Board. All members of the Nominating and Governance Committee qualify as independent under the definition promulgated by The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies.

If a stockholder wishes to nominate a candidate to be considered for election as a director at the 2019 annual meeting of stockholders using the procedures set forth in theBy-laws, it must follow the procedures described below under “Stockholder Proposals and Nominations for Director” at the end of this proxy statement.

In addition, the Nominating and Governance Committee may consider candidates recommended by stockholders, as well as from other sources, such as current directors or officers, third-party search firms or other appropriate sources. For all potential candidates, the Nominating and Governance Committee may consider all factors it deems relevant, such as a candidate’s personal integrity and sound judgment, business and professional skills and experience, independence, knowledge of the biotechnology industry, possible conflicts of interest, diversity, the extent to which the candidate would fill a present need on the Board, and concern for the long-term interests of the stockholders. In general, persons recommended by stockholders will be considered on the same basis as candidates from other sources. If a stockholder wishes simply to propose a candidate for consideration as a nominee by the Nominating and Governance Committee, it should submit any pertinent information regarding the candidate to the Chairman of the Nominating and Governance Committee by mail at 701 Gateway Boulevard, Suite 210, South San Francisco, California 94080. The Nominating and Governance Committee considers issues of diversity among its members in identifying and considering nominees for director, and strives where appropriate to achieve a diverse balance of backgrounds, perspectives, experience, age, gender, ethnicity and country of citizenship of the Board and its committees.

A copy of the Nominating and Governance Committee’s written charter is publicly available on our website at www.mateon.com.

Board of Directors Leadership Structure

The Board does not have a policy regarding the separation of the roles of CEO and Chairman of the Board, as the Board believes it is in the best interests of the Company to periodically make that determination based on the position and direction of the Company and the membership of the Board. The Board has determined that having an employee director serve as Chairman is in the best interest of the Company’s stockholders at this time.

The Chairman of the Board of Directors provides leadership to the Board and works with the Board to define its activities and the calendar for fulfillment of its responsibilities. The Chairman of the Board of Directors approves the meeting agendas after input from management, facilitates communication among members of the Board and presides at meetings of our Board and stockholders. Dr. Schwieterman has served as Chairman of the Board of Directors since August 18, 2016.

The Chairman of the Board of Directors, the Chairman of the Audit Committee, the CEO and the other members of the Board work in concert to provide oversight of our management and affairs. We believe that the leadership of the Chairman of the Board fosters a culture of open discussion and deliberation, with a thoughtful evaluation of risk, to support our decision-making. Our Board encourages communication among its members and between management and the Board to facilitate productive working relationships. Working with the other members of the Board, the Chairman also works to ensure that there is an appropriate balance and focus among key board responsibilities such as strategic development, review of operations and risk oversight.

The Board of Directors’ Role in Risk Oversight

The Board plays an important role in risk oversight through direct decision-making authority with respect to significant matters and the oversight of management by the Board and its committees. In particular, the Board administers its risk oversight function through (1) the review and discussion of regular periodic reports to the Board and its committees on topics relating to the risks that we face, (2) the required approval by the Board (or a committee of the Board) of significant transactions and other decisions, (3) the direct oversight of specific areas of our business by the Audit and Compensation Committees, and (4) regular periodic reports from our auditors and outside advisors regarding various areas of potential risk, including, among others, those relating to our internal control over financial reporting. The Board also relies on management to bring significant matters impacting us to the Board’s attention.

Pursuant to the Audit Committee’s charter, the Audit Committee is responsible for discussing the guidelines and policies that govern the process by which our exposure to financial risk is assessed and managed by management. As part of this process, the Audit Committee discusses our major financial risk exposures and steps that management has taken to monitor, control, and report such exposure. In addition, we, under the supervision of the Audit Committee, have established procedures available to all employees for the anonymous and confidential submission of complaints relating to any matter to encourage employees to report questionable activities directly to our senior management and the Audit Committee. Because of the role of the Board in risk oversight, the Board believes that any leadership structure that it adopts must allow it to effectively oversee the management of the risks relating to our operations. The Board recognizes that there are different leadership structures that could allow it to effectively oversee the management of the risks relating to our operations; however, the Board believes its current leadership structure enables it to effectively provide oversight with respect to such risks.

Stockholder Communications to the Board

Generally, stockholders who have questions or concerns should contact our Investor Relations department at (650)635-7000. However, any stockholders who wish to address questions regarding our business directly with the Board of Directors, or any individual director, should submit his or her questions to the appropriate director using the Investor Relations email link in the “Contact Us” section on the Company’s website at www.mateon.com. Communications will be distributed to the Board, or to any individual director or directors as appropriate, depending on the facts and circumstances outlined in the communications. Items that are unrelated to the duties and responsibilities of the Board may be excluded, such as:

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In addition, any material that is unduly hostile, threatening, or illegal in nature may be excluded, provided that any communication that is filtered out will be made available to any outside director upon request.

Our whistleblower hotline is accessible by telephone at844-990-0002, bye-mail at reports@lighthouse-services.com, and online at http://www.lighthouse-services.com/Mateon.

EXECUTIVE OFFICERS OF THE COMPANY

See “Proposal 1 – Election of Directors” above for the biography of our President and Chief Executive Officer, William D. Schwieterman, M.D.

Matthew M. Loar, age 55, was appointed as our Chief Financial Officer in July 2015. Mr. Loar was previously Chief Financial Officer of KineMed, Inc., a privately held biotechnology company, from January 2014 to July 2015. From January 2010 to January 2014, Mr. Loar was an independent financial consultant to companies in the biopharmaceutical industry. While consulting, he also served as acting Chief Executive Officer and Chief Financial Officer of Neurobiological Technologies, Inc. (NTI), a publicly traded pharmaceutical company, beginning in February 2010 and currently continuing, and as Chief Financial Officer of Virolab, Inc., a biotechnology company, from May 2011 to August 2012. Previously, he was Chief Financial Officer of NTI from April 2008 to December 2009. Earlier in his career, Mr. Loar was Chief Financial Officer of Osteologix, Inc., a publicly traded pharmaceutical company, from 2006 to 2008, and of Genelabs Technologies, Inc., a publicly traded biopharmaceutical and diagnostics company, from 1995 to 2006. Mr. Loar currently serves on the board of directors of NTI. Mr. Loar received a B.A. in Legal Studies from the University of California, Berkeley and is a Certified Public Accountant (inactive) in California. We have an employment agreement with Mr. Loar, as further described under “Execution Compensation – Narrative Disclosure to Summary Compensation Table.”

AUDIT COMMITTEE REPORT

The Audit Committee of the Board of Directors, the members of which have been appointed by the Board of Directors and which consists entirely of directors who meet the independence and experience requirements of The Nasdaq Stock Market and the independence requirements of the OTC Markets’ OTCQX Rules for U.S. Companies, has furnished the following report:

The Audit Committee assists the Board in overseeing and monitoring the integrity of our financial reporting process, compliance with legal and regulatory requirements and the quality of internal and external audit processes. This committee’s role and responsibilities are set forth in our charter adopted by the Board, which is available on our website at www.mateon.com. This committee reviews and reassesses our charter annually and recommends any changes to the Board for approval. The Audit Committee is responsible for overseeing our overall financial reporting process, and for the appointment, compensation, retention, and oversight of the work of OUM & Co. LLP. In fulfilling its responsibilities for the financial statements for 2017, the Audit Committee took the following actions:

Based on the Audit Committee’s review of the audited financial statements and discussions with management and OUM & Co. LLP, the Audit Committee recommended to the Board that the audited financial statements be included in our Annual Report on Form10-K for the year ended December 31, 2017, for filing with the SEC.

RESPECTFULLY SUBMITTED,

Members of the Mateon Therapeutics, Inc. Audit Committee

Bobby W. Sandage, Jr., Ph.D.

Simon C. Pedder, Ph.D.

Donald R. Reynolds

SECTION 16(A) BENEFICIAL OWNERSHIP REPORTING COMPLIANCE

Section 16(a) of the Exchange Act requires our directors, executive officers and persons who own more than 10% of our common stock to file with the SEC and us initial reports of beneficial ownership and reports of changes in beneficial ownership of our common stock and other equity securities. For these purposes, the term “other equity securities” would include options granted under the 2005 Stock Plan, the 2015 Plan and the 2017 Plan. To our knowledge, based solely on a review of the forms and written representations received by us from our Section 16 reporting persons, during the year ended December 31, 2017, all Section 16(a) filing requirements applicable to the reporting persons were properly and timely satisfied.

CERTAIN RELATIONSHIPS AND RELATED PERSON TRANSACTIONS

Our Audit Committee reviews and approves in advance all related person transactions.

Our Board of Directors has reviewed the materiality of any relationship that each of our directors has with the Company, either directly or indirectly. Based upon this review, our Board has determined that each of the nominees except for Dr. Chaplin and Dr. Schwieterman qualify as “independent directors” as defined under the rules of The Nasdaq Stock Market and OTC Markets’ OTCQX Rules for U.S. Companies.

Dr. Chaplin is a resident of the United Kingdom, and during 2016 the services he performed for Mateon while in the United Kingdom were conducted through Aston Biopharma LTD, an entity which Dr. Chaplin controlled, while the payment for services Dr. Chaplin performed for Mateon while he was in the United States were made directly to Dr. Chaplin. We paid Aston Biopharma LTD approximately $105,750 as compensation for services Dr. Chaplin performed while he was in the United Kingdom during 2016, and his compensation for services as an employee was reduced by this amount. Aston Biopharma LTD and Mateon terminated the consultancy agreement effective as of January 1, 2017 and all payments for Dr. Chaplin’s services were thereafter made directly to Dr. Chaplin. The compensation Dr. Chaplin has received from the Company is further described under “Executive Compensation”, and includes compensation received under the consultancy agreement with Aston Biopharma LTD.

On April 12, 2018, we closed a private placement transaction in which we received net proceeds of approximately $2.4 million. The private placement transaction consisted of the sale of 58.5 units at a purchase price of $50,000 per unit, and each unit contained 250,000 shares of our common stock and warrants to purchase up to 250,000 shares of our common stock. The purchase price of the common stock was $0.20 per share and warrants are exercisable at $0.40 per share. Dr. Schwieterman purchased 2.5 units and Mr. Loar and Mr. Reynolds each purchased one unit in the private placement transaction. The purchases of Dr. Schwieterman, Mr. Loar and Mr. Reynolds were reviewed in advance by disinterested directors on the Audit Committee.

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The following tables set forth certain information with respect to the beneficial ownership of our common stock as of September 15, 2016,April 12, 2018 for (a) each of our named executive officers listednamed in our proxy statement for the 2016 annual meeting of stockholders held on June 1, 2016,Summary Compensation Table, (b) each of our directors, (c) all of our current directors and executive officers as a group, and (d) each stockholder known by us to own beneficially more than 5% of our common stock. Beneficial ownership is determined in accordance with the rules of the SEC and includes voting or investment power with respect to the securities. We deem shares of common stock that may be acquired by an individual or group within 60 days of September 15, 2016April 12, 2018 pursuant to the exercise of options or warrants to be outstanding for the purpose of computing the percentage ownership of such individual or group, but such shares are not deemed to be outstanding for the purpose of computing the percentage ownership of any other person shown in the tables. Except as indicated in footnotes to these tables, we believe that the stockholders named in these tables have sole voting and investment power with respect to all shares of common stock shown to be beneficially owned by them based on information provided to us by these stockholders. Ownership determinations are based on 26,544,93441,169,934 shares of common stock outstanding on September 15, 2016.April 12, 2018. Unless otherwise indicated, the address of each stockholder is c/o Mateon Therapeutics, Inc., 701 Gateway Boulevard, Suite 210, South San Francisco, CA 94080.

The determination that there were no other persons, entities or groups known to us to beneficially own more than 5% of our outstanding common stock as of September 15, 2016,April 12, 2018, was based on a review of all statements filed with respect to us since the beginning of the past fiscal year with the SEC pursuant to Section 13(d) or 13(g) of the Exchange Act.

EXECUTIVE COMPENSATION

Summary Compensation Table

The following table shows the total compensation paid or accrued during 2017 and 2016 to (1) our President and Chief Executive Officer, (2) our Chief Financial Officer and (3) our Chief Scientific Officer, the latter two of which are our next most highly compensated executive officers earning more than $100,000 in 2017.

On October 2, 2017, the Company and Dr. Schwieterman agreed to a 50% reduction in his base annual salary (to $205,000), with reinstatement to previous levels contingent on the Company raising additional funding of at least $4 million or the execution of a licensing or collaboration agreement with certain conditions. Dr. Schwieterman continues to receive the reduced salary as of the date of the filing of this proxy statement.

Dr. Schwieterman may terminate his employment upon written notice to us. We may terminate his employment without prior written notice for cause, or without cause on sixty days’ prior written notice. If his employment is terminated by us for cause, by reason of his death or disability or by Dr. Schwieterman without good reason, we will pay him the amount of our accrued obligations as of the date of such termination. If his employment is terminated by us other than for cause or by Dr. Schwieterman with good reason, we will pay him the accrued obligations, an amount equal to twelve months of his then-current base salary and twelve months of health insurance premiums pursuant to the Consolidated Omnibus Budget Reconciliation Act of 1985 (“COBRA”), subject to the conditions outlined in the agreement.

If his employment is terminated by us other than for cause or by Dr. Schwieterman with good reason in the one year following the effective date of a change in control of the Company, we will pay him our accrued obligations, an amount equal to twelve months of his then-current base salary and twelve months of COBRA premiums on the same conditions described above. In addition, all of his unvested equity awards outstanding on the date of termination shall vest and be immediately exercisable. Dr. Schwieterman has also agreed not to directly or indirectly solicit for employment, during his employment and for a twelve month period following termination of his employment, any person who is (or has been in the past year) a Company officer, executive or key employee.

All payments made and benefits available to Dr. Schwieterman in connection with his employment agreement will comply with Internal Revenue Code Section 409A in accordance with the terms of his employment agreement.

On March 21, 2016, the Company granted Dr. Schwieterman options to purchase 500,000 shares of our common stock with an exercise price of $0.7277 per share, which vest over a four year period. On January 12, 2017, the Company granted Dr. Schwieterman options to purchase 550,000 shares of our common stock with an exercise price of $0.375 per share, which vest over a four year period.

Matthew M. Loar. On July 20, 2015, we entered into an employment agreement with Mr. Loar for his service as our Chief Financial Officer. Pursuant to the terms of this agreement, Mr. Loar is entitled to receive an annual base salary of $325,000. In addition, he is eligible for an annual bonus of up to thirty-five percent of his then-current annual base salary, based on the Board of Directors’ assessment of his performance and the Company’s performance. For calendar year 2016, the Board of Directors determined that Mr. Loar’s annual bonus would be at 50% of the targeted level, and for calendar year 2017, the Board of Directors determined that he would not receive an annual bonus due to the financial condition of the Company.

On October 2, 2017, the Company and Mr. Loar agreed to a 50% reduction in his base annual salary (to $162,500), with reinstatement to previous levels contingent on the Company raising additional funding of at least $4 million or the execution of a licensing or collaboration agreement with certain conditions. Mr. Loar continues to receive the reduced salary as of the date of the filing of this proxy statement.

Mr. Loar may terminate his employment agreement upon written notice to us. We may terminate the employment agreement without prior written notice for cause, or without cause on sixty days’ prior written notice. If his employment is terminated by us for cause, by reason of his death or disability or by Mr. Loar without good reason, we will pay him the amount of our accrued obligations, as of the date of such termination. If his employment is terminated by us other than for cause or by Mr. Loar with good reason, we will pay him the accrued obligations, an amount equal to twelve months of his then-current base salary and twelve months of health insurance premiums pursuant to COBRA, subject to the conditions outlined in the agreement.

If his employment is terminated by us other than for cause or by Mr. Loar with good reason in the one year following the effective date of a change in control of the Company, we will pay him our accrued obligations, an amount equal to twelve months of his then-current base salary and twelve months of COBRA premiums on the same conditions described above. In addition, all of his unvested equity awards outstanding on the date of termination shall vest and be immediately exercisable. Mr. Loar has also agreed not to directly or indirectly solicit for employment, during his employment and for a twelve month period following termination of his employment, any person who is (or has been in the past year) a Company officer, executive or key employee.

All payments made and benefits available to Mr. Loar in connection with his employment agreement will comply with Internal Revenue Code Section 409A in accordance with the terms of his employment agreement.

On March 21, 2016, the Company granted Mr. Loar options to purchase 262,500 shares of our common stock with an exercise price per share of $0.7277 per share, which vest over a four year period. On January 12, 2017, the Company granted Mr. Loar options to purchase 350,000 shares of our common stock with an exercise price of $0.375 per share, which vest over a four year period.

Dr. David J. Chaplin. On May 12, 2015 we entered into an amended and restated employment agreement with Dr. Chaplin for his services as our Chief Scientific Officer. Pursuant to the terms of his employment agreement, Dr. Chaplin is entitled to receive an annual base salary of $220,000. In addition, he is eligible to be awarded an annual bonus of up to thirty-five percent of his then-current annual base salary, based on the Board of Directors’ assessment of his performance and the Company’s performance. For calendar year 2016, the Board of Directors determined that Dr. Chaplin’s annual bonus would be at 50% of the targeted level, and for calendar year 2017, the Board of Directors determined that he would not receive an annual bonus due to the financial condition of the Company.

On October 2, 2017, the Company and Dr. Chaplin agreed to a 50% reduction in his base annual salary (to $110,000), with reinstatement to previous levels contingent on the Company raising additional funding of at least $4 million or the execution of a licensing or collaboration agreement with certain conditions. Dr. Chaplin continued to receive the reduced salary through his retirement from employment with the Company on January 11, 2018.

On March 21, 2016, we granted Dr. Chaplin options to purchase 262,500 shares of our common stock with an exercise price per share of $0.7277 per share which were scheduled to vest over a four year period. On January 12, 2017, the Company granted Dr. Chaplin options to purchase 262,500 shares of our common stock with an exercise price of $0.375 per share, which were scheduled to vest over a four year period. The unvested portion of these options terminated following Dr. Chaplin’s retirement.

Outstanding Equity Awards at FiscalYear-End

The following table shows all outstanding grants of stock options as of December 31, 2017 to each of the executive officers named in the Summary Compensation Table. There were no grants of unvested stock awards outstanding as of December 31, 2017.

William D. Schwieterman, M.D.

Matthew M. Loar

In each such case the Change of Control must also meet the requirements of a “Change of Control Event” within the meaning of Section 409(a)(2)(A)(v) of the Code.

Each of Dr. Schwieterman and Mr. Loar will be entitled to certain benefits as described in the table above if his employment is terminated by the Company for reasons other than cause or by him with good reason. “Cause,” as defined in the employment agreements, means:

“Good Reason,” as defined in the employment agreements, means the Company:

Good Reason must also meet the requirements for a good reason termination in accordance with Code Section 409A, and any successor statute, regulation and guidance thereto.

Director Compensation

The following table shows the total compensation paid or accrued during 2017 to each of ournon-employee directors. Directors who are employed by us are not compensated for their service on our Board of Directors.

Although the above options vest one year subsequent to grant, pursuant to rules of the SEC the values in the table represents the full value at the grant date only and the values do not take into account subsequent increases or decreases in actual value to the recipient. See Note 6 to our Financial Statements included in our Annual Report on Form10-K for the year ended December 31, 2017, for additional information regarding the assumptions used to determine the fair value of each of the option awards in this table. See also our discussion of stock-based compensation under “Management’s Discussion and Analysis of Financial Condition and Results of Operations – Critical Accounting Policies and Significant Judgments and Estimates” in the Form10-K.

The following is a description of the standard compensation arrangements under which ournon-employee directors are compensated for their service as directors, including as members of the various Committees of our Board.

Fees. In July 2014, the Board of Directors adopted a director compensation policy, which was amended and restated on October 25, 2016, (as amended and restated, the “2016 Director Compensation Policy”). In accordance with the 2016 Director Compensation Policy, the following cash fees are payable tonon-employee directors quarterly in arrears at the end of each quarter:

A newnon-employee director joining the Board during the course of the year on a date other than the first day of the quarter will receive his or her cash compensation for that quarterpro-rated.

In October 2017, the Board of Directors suspended all cash payments for board service until the Company’s financial position improved sufficiently to warrant reinstatement of cash fees. As of the date of the filing of this proxy statement, board members continue to receive no fees.

Equity Grants. In accordance with the 2016 Director Compensation Policy, on the date of each annual meeting, eachnon-employee director is granted anon-qualified stock option to purchase shares of our common stock valued at $40,000 on the date of grant, which will vest in full one year from the grant date, subject to the applicable director’s continued service on the Board as of the vesting date.

A newnon-employee director joining the Board will be granted an option to purchase shares of our common stock valued at $50,000 on or shortly after the first date of his or her service, which will vest over a three year period subject to the director’s continued service on the Board as of each vesting date.

Each option granted under the 2016 Director Compensation Policy will have an exercise price equal to the closing price of our common stock on OTCQX marketplace (or other applicable trading market) on the date of grant, or if the date of grant is not a trading day, the closing price on the next trading day following the date of grant, and each option will have a term of six years. The number of options to be received under the 2016 Director Compensation Policy will be calculated using the Black-Scholes valuation method.

Options granted pursuant to the 2016 Director Compensation Policy are subject to the terms and conditions of the applicable stock plan. Under the terms of the 2015 Incentive Plan and the 2017 Incentive Plan, directors may be granted shares of common stock, stock-based awards, and/or stock options to purchase shares of common stock.

Summary Description of the Company’s 2017 Plan

On January 12, 2017, the Board of Directors, with the approval of the Compensation Committee of the Board, adopted and approved the Mateon Therapeutics, Inc. 2017 Equity Incentive Plan (the “2017 Plan”). The following is a summary of the 2017 Plan, which is qualified in its entirety by reference to the text of the 2017 Plan and the form of option agreement under the 2017 Plan, copies of which are attached as Exhibits 10.1 and 10.2, respectively, to the Company’s Form8-K, filed with the SEC on January 13, 2017.

Eligibility. The 2017 Plan allows us, under the direction of our Compensation Committee, to make grants of stock options, restricted and unrestricted stock awards, and other stock-based awards to employees, consultants and directors. The purpose of these awards is to attract and retain key individuals, further align employee and stockholder interests, and provide additional incentive for them to promote our success or the success of our affiliates.

Shares Available for Issuance. The 2017 Plan provides for the issuance of up to 2,000,000 shares of our common stock. Generally shares of common stock reserved for awards under the 2017 Plan that lapse or are cancelled, forfeited, surrendered or terminated for any reason will be added back to the share reserve available for future awards. However, shares of common stock tendered in payment for an award or shares of common stock withheld for taxes will not be available again for grant.

Stock Options. Stock options granted under the 2017 Plan must benon-qualified stock options, which are not intended to meet the requirements of Section 422 of the Internal Revenue code. Award agreements for stock options include rules for exercise of the stock options after termination of service. Options may not be exercised unless they are vested, and no option may be exercised after the end of the term set forth in the award agreement. Generally, stock options will be exercisable for three months after termination of service for any reason other than death or total and permanent disability, and for twelve months after termination of service on account of death or total and permanent disability.

Restricted Stock. Restricted stock is common stock that is subject to restrictions, including a prohibition against transfer and a substantial risk of forfeiture, until the end of a “restricted period” during which the grantee must satisfy certain vesting conditions. If the grantee does not satisfy the vesting conditions by the end of the restricted period, the restricted stock is forfeited. During the restricted period, the holder of restricted stock has the rights and privileges of a regular stockholder, except that the restrictions set forth in the applicable award agreement apply. For example, the holder of restricted stock may vote and receive dividends on the restricted shares; but he or she may not sell the shares until the restrictions are lifted.

Other Stock-Based Awards. The 2017 Plan also authorizes the grant of other types of stock-based compensation including, but not limited to stock appreciation rights, phantom stock awards, and stock unit awards. Our Compensation Committee may award such stock-based awards subject to such conditions and restrictions as it may determine. These conditions and restrictions may include continued employment with us through a specified restricted period.

Plan Administration. In accordance with the terms of the 2017 Plan, our Board of Directors has authorized our Compensation Committee to administer the 2017 Plan. The Compensation Committee may delegate part of its authority and powers under the 2017 Plan to one or more of our directors and/or officers, but only our Board of Directors or our Compensation Committee can make awards to participants who are directors or executive officers of the Company. In accordance with the provisions of the 2017 Plan, our Compensation Committee determines the terms of awards, including, which employees, directors and consultants will be granted awards, the number of shares subject to each award, the vesting provisions of each award, the termination and cancellation provisions applicable to awards, and all other terms and conditions upon which each award may be granted in accordance with the 2017 Plan. In addition, our Compensation Committee may, in its discretion, amend any term or condition of any outstanding award, other than reducing the exercise price or purchase price, provided that (i) the term or condition as amended is not prohibited by the 2017 Plan; (ii) any amendment does not impair the rights of a participant under any award previously granted without that participant’s consent; and (iii) any amendment will be made only after the Compensation Committee determines whether the amendment would cause any adverse tax consequences to the participant.

Stock Dividends and Stock Splits. If our common stock shall be subdivided or combined into a greater or smaller number of shares or if we issue any shares of common stock as a stock dividend, the number of shares of our common stock deliverable upon exercise of an option issued or upon issuance of an award shall be appropriately increased or decreased proportionately, and appropriate adjustments shall be made in the purchase price per share to reflect such subdivision, combination, or stock dividend.

Corporate Transactions. Upon a merger or other reorganization event, the Compensation Committee or the successor board, may, in its sole discretion, take any one or more of the following actions pursuant to the 2017 Plan, as to some or all outstanding awards (i) to provide that all outstanding options shall be assumed or substituted by the successor corporation, (ii) upon written notice to a participant, to provide that the participant’s unexercised options will terminate immediately prior to the consummation of such transaction unless exercised by the participant, (iii) in the event of a merger pursuant to which holders of our common stock will receive a cash payment for each share surrendered in the merger, to make or provide for a cash payment to the participants equal to the difference between the merger price times the number of shares of our common stock subject to such outstanding options, and the aggregate exercise price of all such outstanding options, in exchange for the termination of such options, (iv) to provide that outstanding awards shall be assumed or substituted by the successor corporation, become realizable or deliverable, or restrictions applicable to an award will lapse, in whole or in part, prior to or upon the merger or reorganization event, and (v) with respect to stock grants and in lieu of any of the foregoing, the Compensation Committee or the successor board may provide that, upon consummation of the transaction, each outstanding stock grant shall be terminated in exchange for payment of an amount equal to the consideration payable upon consummation of such transaction to a holder of the number of shares of common stock comprising such award (to the extent such stock grant is no longer subject to any forfeiture or repurchase rights then in effect or, at the discretion of the Compensation Committee, all forfeiture and repurchase rights being waived upon such transaction).

Amendment and Termination. The 2017 Plan may be amended by the Compensation Committee, in their capacity as administrator of the 2017 Plan. However, no such action may adversely affect any rights under any outstanding award without the holder’s consent.

Duration of Plan. The 2017 Plan will expire by its terms on January 12, 2027.

Federal Income Tax Considerations. The material federal income tax consequences of the issuance and exercise of stock options and other awards under the 2017 Plan, based on the current provisions of the Code and regulations, are as follows. Changes to these laws could alter the tax consequences described below. This summary assumes that all awards granted under the 2017 Plan are exempt from or comply with, the rules under Section 409A of the Code related to nonqualified deferred compensation.

Non-Qualified Options.Non-qualified options may be granted under the 2017 Plan. Anon-qualified option ordinarily will not result in income to the optionee or deduction to us at the time of grant. The optionee will recognize compensation income at the time of exercise of suchnon-qualified option in an amount equal to the excess of the then value of the shares over the option price per share. Such compensation income of optionees may be subject to withholding taxes, and a deduction may then be allowable to us in an amount equal to the optionee’s compensation income. An optionee’s initial basis in shares so acquired will be the amount paid on exercise of thenon-qualified option plus the amount of any corresponding compensation income. Any gain or loss as a result of a subsequent disposition of the shares so acquired will be capital gain or loss.

Stock Grants. With respect to stock grants under the 2017 Plan that result in the issuance of shares that are either not restricted as to transferability or not subject to a substantial risk of forfeiture, the grantee must generally recognize ordinary income equal to the fair market value of shares received. Thus, deferral of the time of issuance will generally result in the deferral of the time the grantee will be liable for income taxes with respect to such issuance. We generally will be entitled to a deduction in an amount equal to the ordinary income recognized by the grantee. With respect to stock grants involving the issuance of shares that are restricted as to transferability and subject to a substantial risk of forfeiture, the grantee must generally recognize ordinary income equal to the fair market value of the shares received at the first time the shares become transferable or are not subject to a substantial risk of forfeiture, whichever occurs earlier. A grantee may elect to be taxed at the time of receipt of shares rather than upon lapse of restrictions on transferability or substantial risk of forfeiture, but if the grantee subsequently forfeits such shares, the grantee would not be entitled to any tax deduction, including as a capital loss, for the value of the shares on which he previously paid tax. The grantee must file such election with the Internal Revenue Service within 30 days of the receipt of the shares. We generally will be entitled to a deduction in an amount equal to the ordinary income recognized by the grantee.

Stock Units. The grantee recognizes no income until the issuance of the shares. At that time, the grantee must generally recognize ordinary income equal to the fair market value of the shares received. We generally will be entitled to a deduction in an amount equal to the ordinary income recognized by the grantee.

EXPENSES OF SOLICITATION

We will bear the costs of soliciting proxies from our stockholders. We will make this solicitation by mail, and our directors, officers, and employees may also solicit proxies by telephone, fax, e-mail or in person, for which they will receive no compensation other than their regular compensation as directors, officers, or employees. As noted above in “What are the Costs of Soliciting These Proxies,” Morrow & Co., LLC has been engaged to act as our proxy solicitor in connection with the proposals to be acted upon at the Special Meeting. For these services, we will pay Morrow & Co., LLC a fee of approximately $7,500 plus expenses. Arrangements will also be made with brokerage houses and other custodians, nominees and fiduciaries to send proxies and proxy materials to beneficial owners of our voting securities. We will reimburse these brokerage firms, custodians, nominees and fiduciaries for reasonableout-of-pocket expenses that are incurred by them.

COMPENSATION PRACTICES AND POLICIES RELATING TO RISK MANAGEMENT

Consistent with SEC disclosure requirements, we have assessed our compensation policies, practices and awards, and have concluded that our compensation policies, practices and awards do not create risks that are reasonably likely to have a material adverse effect on the Company. Management and the Compensation Committee of our Board of Directors each assessed our compensation and benefits programs to determine if the programs’ provisions and operations create undesired or unintentional risk of a material nature. Our compensation programs include a combination of fixed base salaries, cash bonuses, long-term incentive awards, including performance-based compensation, and employee retirement plans that are generally uniform in design and operation throughout the Company and with all levels of employees.

Based on the foregoing, we believe that our compensation policies, practices and awards do not create risks that are likely to have a material adverse effect on the Company as a whole. We also believe that our incentive compensation arrangements provide incentives that do not encourage risk-taking beyond the organization’s ability to effectively identify and manage significant risks, are compatible with our effective internal controls and our risk management practices, and are supported by the oversight and administration of the Compensation Committee with regard to executive compensation programs.

CORPORATE CODE OF CONDUCT AND ETHICS

We have adopted a Corporate Code of Conduct and Ethics (the “Code of Conduct”) that applies to all of our employees, including our CEO and CFO. The text of the Code of Conduct has been filed as an exhibit to our Annual Report on Form10-K for the year ended December 31, 2014, and is posted on our website at www.mateon.com. Disclosure regarding any amendments to, or waivers from provisions of the code of conduct and ethics that apply to our directors, principal executive, and financial officers will be included in a Current Report on Form8-K within four business days following the date of the amendment or waiver.

STOCKHOLDER PROPOSALS AND NOMINATIONS FOR DIRECTOR

FOR THE NEXT ANNUAL MEETING

Your eligibility as a stockholder to submit proposals and director nominations, the proper subjects of such proposals and other issues governing stockholder proposals and director nominations are regulated by the rules adopted under Section 14 of the Exchange Act and our By-laws. To be considered for inclusion in the proxy statement relating to our next annual meeting2019 Annual Meeting of stockholdersStockholders, we must receive stockholder proposals (other than for director nominations) no later than Monday, January 7, 2019. To be considered for presentation at the 2019 Annual Meeting, although not included in the proxy statement, proposals (including director nominations that are not requested to be heldincluded in 2017, stockholder proposals and nominationsour proxy statement) must be received no earlier than 75 days prior to the date that is one year from this year’s mailing date and no later than April 17, 2017 and no earlier than March 18, 2017.45 days prior to the date that is one year from this year’s mailing date. Proposals that are not received in a timely manner will not be voted on at the 2019 Annual Meeting. If a proposal is received on time, the proxies that management solicits for the meeting may still exercise discretionary voting authority on the proposal under circumstances consistent with the proxy rules of the SEC. All stockholder proposals should be marked for the attention of The Secretary, Mateon Therapeutics, Inc., 701 Gateway Boulevard, Suite 210, South San Francisco, California 94080.

OTHER MATTERS

The Board of Directors knows of no other business that will be presented at the SpecialAnnual Meeting. If any other business is properly brought before the SpecialAnnual Meeting, it is intended that proxies in the enclosed form will be voted in accordance with the judgment of the persons voting the proxies.

ANNUAL REPORT

Our Annual Report on Form10-K for the year ended December 31, 2017, which includes our financial statements, provides additional information about us and can be found on the website of the SEC at www.sec.gov. They are also available on our website at www.mateon.com. You may obtain a printed copy of our Annual Report on Form10-K, including our financial statements, free of charge, from us by sending a written request to: Mateon Therapeutics, Inc., 701 Gateway Boulevard, Suite 210, South San Francisco, California 94080, Attention: Investor Relations.

South San Francisco, CA

September [●], 2016May 7, 2018