UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM10-K/A

(Amendment No. 1)

(Mark One)

For the fiscal year ended December 31, 20182021

OR

FOR THE TRANSITION PERIOD FROM TO

Commission FileNumber 001-38663

Gritstone Oncology,bio, Inc.

(Exact name of Registrant as specified in its Charter)

(510)(510) 871-6100

Registrant’s telephone number, including area code

Securities registered pursuant to Section 12(b) of the Act:

Securities Registered Pursuant to Section 12(g) of the Act: None

Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. YESYes ☐ NONo ☒

Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. YESYes ☐ NO  No☒

Indicate by check mark whether the Registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. YESYes ☒ NONo ☐

Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 ofRegulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the Registrant was required to submit such files). YESYes ☒ NONo ☐

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 ofRegulation S-K (§229.405) is not contained herein, and will not be contained, to the best of Registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of thisForm 10-K or any amendment to thisForm 10-K.    ☒

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, anon-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☒

Indicate by check mark whether the Registrant has filed a report on and attestation to its management assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ☐

Indicate by check mark whether the Registrant is a shell company (as defined inRule 12b-2 of the Exchange Act). YES  Yes☐    NONo ☒

The aggregate market value of the common stock held by non-affiliates of the registrant was not a public company as of theJune 30, 2021 (the last business day of itsthe registrant’s most recently completed second fiscal quarterquarter) was approximately $419.0 million, based on the closing price of the registrant’s common stock, as reported by the Nasdaq Global Select Market on June 30, 2021 of $9.13 per share. Shares of the registrant’s common stock held by each executive officer, director, and therefore, cannot calculateholder of 5% or more of the aggregate market valueoutstanding common stock have been excluded in that such persons may deemed to be affiliates. This calculation does not reflect a determination that certain persons are affiliates of its voting andnon-voting common equity held bynon-affiliates as of such date.the registrant for any other purpose.

The number of shares of Registrant’s Common Stock outstanding as of March 22, 20197, 2022 was 29,193,819.72,708,342.

DOCUMENTS INCORPORATED BY REFERENCE

None.Portions of the Registrant’s Definitive Proxy Statement relating to the Annual Meeting of Shareholders, scheduled to be held on June 17, 2022, are incorporated by reference into Part III of this Annual Report on Form 10-K where indicated. Such Definitive Proxy Statement will be filed with the Securities and Exchange Commission on April 28, 2022.

Explanatory NoteEXPLANATORY NOTE

ThisGritstone bio, Inc. (the “Company”, “we”, “our” and “us”) is filing this Amendment No. 1 on Form10-K/A (this “Amendment”(the “Amendment No. 1”) amends thesolely to amend our Annual Report on Form10-K of Gritstone Oncology, Inc. (the “Company,” “Gritstone,” “we,” “us” or “our”) for the fiscal year ended December 31, 2018,2021 (the “Original Filing”), originally filed with the U.S. Securities and Exchange Commission (“SEC”(the “SEC”) on March 28, 201810, 2022 (the “Original Filing”Filing Date”).

This We are filing this Amendment is being filed for the purpose of providing the information required by Items 10 through 14 ofNo. 1 to amend clerical errors made in Part IIII of the Annual Report on Form10-K. This information was previously omitted fromOriginal Filing. The clerical errors were made in the third sentence and the title of Figure 8 included under the heading “Item 1. Business—New Developments—GRANITE updates”.

Item 1. Business.

New Developments

GRANITE updates

On January 13, 2022, we announced the first patient was enrolled for inclusion in the GRANITE -CRC-1L study, a Phase 2/3 trial evaluating our individualized neoantigen vaccine (GRANITE) for first line (1L) maintenance treatment of metastatic, microsatellite-stable colorectal cancer (MSS-CRC).

On January 13, 2022, we also announced updated interim data from the disclosures contained therein to reflect any events that occurred subsequent to the datePhase 1/2 GRANITE trial evaluating individualized immunotherapy in combination with nivolumab (OPDIVO®) and ipilimumab (YERVOY®) in patients with advanced solid tumors. As of the Original Filing.January 5, 2022 data cutoff date, 6 out of 12 MSS-CRC patients treated in such GRANITE trial, who were alive at the time of our ESMO 2021 data presentation on September 17, 2021, remained alive, and the correlation between ctDNA and overall survival continued to be observed (Figure 8).

Table of Contents

SIGNATURES

PART III

ITEM 10. DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE.

Directors

Our board of directors is divided into three classes. Each class consists, as nearly as possible, ofone-third of the total number of directors, and each class has a staggered, three-year term. Unless the board of directors determines that vacancies (including vacancies created by increases in the number of directors) shall be filled by the stockholders, and except as otherwise provided by law, vacancies on the board of directors may be filled only by the affirmative vote of a majority of the remaining directors. A director elected by the board of directors to fill a vacancy (including a vacancy created by an increase in the number of directors) shall serve for the remainder of the full term of the class of directors in which the vacancy occurred and until such director’s successor is elected and qualified.

The board of directors currently consists of seven seated directors, divided into the three following classes:

At each annual meeting of stockholders, the successors to directors whose terms will then expire will be elected to serve from the time of election and qualification until the third subsequent annual meeting of stockholders.

The following table sets forth for our current directors, information with respect to their ages as of March 31, 2019 and position/office held within the Company: 

Set forth below is biographical information for our current directors. The following includes certain information regarding our directors’ individual experience, qualifications, attributes and skills that led the board of directors to conclude that they should serve as directors.

Andrew Allen, M.D., Ph.D.co-founded Gritstone Oncology, Inc. and has served as our President and Chief Executive Officer and a member of our board of directors since September 2015. Prior to Gritstone, in April 2009, Dr. Allenco-founded Clovis Oncology, Inc., a public pharmaceutical development company, and served as its executive vice president of clinical and preclinical development and chief medical officer from April 2009 to July 2015. Prior to that, he was chief medical officer at Pharmion Corporation from 2006 to 2008. Previously, Dr. Allen served in clinical development leadership roles at Chiron Corporation and Abbott Laboratories, and worked at McKinsey & Company, where he advised life science companies on strategic issues. He currently serves on the board of directors of Epizyme, Inc., a publicly traded biopharmaceutical company, Sierra Oncology, Inc., a public biopharmaceutical company, TCR² Therapeutics Inc, a public biopharmaceutical company, and Revitope Inc., a privately-held biotechnology company. Dr. Allen previously served on the board of directors of Cell Design Labs, a private biotechnology company, from November 2015 until its acquisition by Gilead Sciences, Inc. in December 2017. Dr. Allen qualified in medicine at Oxford University and received a Ph.D. in immunology from Imperial College of Science, Technology and Medicine in London. We believe Dr. Allen is qualified to serve on our board of directors due to his educational experience and his experience as a senior executive of biotechnology and pharmaceutical companies, including his service as our chief executive officer.

Richard Heyman, Ph.D. has served as a member of our board of directors since November 2015. Dr. Heyman is executive chairman andco-founder of Metacrine, Inc., a biotechnology company developing new therapeutics for the treatment of liver and gastrointestinal diseases. He also is theco-founder and chairman of ORIC Pharmaceuticals, which is developing drugs to overcome resistance in cancer. Previously, Dr. Heyman served as president and chief executive officer of Seragon Pharmaceuticals Inc., or Seragon, a privately-held biotechnology company, which was acquired by Genentech in 2014. Prior to Seragon, heco-founded and served as president and chief executive officer of Aragon Pharmaceuticals, Inc., or Aragon, until it was purchased by Johnson & Johnson in 2013. He has been involved in the discovery and development of multiple therapeutic agents approved by the FDA, including the recently approved prostate cancer drug, Erleada. Dr. Heyman is a venture partner for Arch Ventures and serves on the Board of Directors for Ymanity Therapeutics and Vividion Therapeutics. He is Vice Chair of the Board of Trustees at the Salk Institute, on the Board Foundation for the American Association for Cancer Research, or AACR, and on the executive committee at the University of California at San Diego Moores Cancer Center. He has won numerous awards including Ernst and Young San Diego Regional Entrepreneur of the Year and the Endocrine Society Outstanding Innovation Award. Dr. Heyman received a B.S. in chemistry from the University of Connecticut and a Ph.D. in pharmacology from the University of Minnesota. He was an NIH post-doctoral fellow and staff scientist at the Salk Institute. We believe that Dr. Heyman is qualified to serve on our board of directors due to his educational background and his experience as a board member and senior executive of biotechnology and pharmaceutical companies.

Steve Krognes has served as a member of our board of directors since July 2018. Mr. Krognes has served as chief financial officer of Denali Therapeutics Inc., or Denali, since October 2015. Mr. Krognes joined Denali from Genentech, where he served as chief financial officer and a member of the executive committee from April 2009 to September 2015. Mr. Krognes also oversaw Genentech’s site services organization between 2011 and 2015, and Genentech’s information technology organization between 2009 and 2011. He chaired the Genentech Access to Care Foundation between 2009 and 2015. From January 2004 to April 2009, Mr. Krognes served as head of mergers and acquisitions and a member of the finance executive committee at Roche, a Swiss biotechnology company. From July 2002 to December 2003, Mr. Krognes served as director of mergers and acquisitions at Danske Bank based in Norway. From April 2000 to June 2002, he was a venture capitalist with Pylonia Ventures, a Swedish venture investments company. Prior to that, Mr. Krognes worked as a consultant at McKinsey & Company and an investment banker at Goldman Sachs, based in London and Boston. Mr. Krognes currently serves as a member of the boards of directors of Corvus Pharmaceuticals, a publicly traded biopharmaceutical company, and RLS Global AB, a Swedish life sciences company. Mr. Krognes served as a board member of the California Life Sciences Association between 2010 and 2015, and the California Academy of Sciences, a private scientific and educational institution, between 2014 and 2018. He received his M.B.A. from Harvard Business School and his B.S. in economics from the Wharton School of the University of Pennsylvania. We believe Mr. Krognes is qualified to serve on our board of directors due to his experience as a board member and senior executive of biotechnology and pharmaceutical companies.

Judith Li has served as a member of our board of directors since September 2017. Ms. Li has served as a partner at Lilly Asia Ventures, or LAV, which is based in Hong Kong and Shanghai and focuses on early and growth stage investments across biopharmaceuticals, medical devices, and diagnostics both domestically and cross-border, since 2013. Judith currently holds board appointments at a variety of LAV’s private portfolio companies, including Just Biotherapeutics, Inc., Veritas Genetics Inc., and Nextcure, Inc. From April 2014 to October 2017, she served on the board of Crown BioScience Inc., a biotechnology company which was publicly listed on the Taiwan

Stock Exchange until it was acquired in December 2017. Currently, Ms. Li serves on the board of directors of Inhibrx, Inc. a public biopharmaceutical company. Previously, Ms. Li served as a senior business analyst at McKinsey & Company, worked in hospital administration at Partners Healthcare, andco-founded an interventional nephrology medical device venture. Judith holds a B.A. in biology from Harvard and an M.B.A. from Harvard Business School. We believe that Ms. Li is qualified to serve on our board of directors due to her experience as a board member of biotechnology and pharmaceutical companies, and her experience as an investor in new life sciences companies.

Nicholas Simon has served as a member of our board of directors since September 2015. Mr. Simon is a Senior Managing Director in the Blackstone Life Sciences group, having joined Blackstone as part of its acquisition of Clarus Ventures, LLC, or Clarus, in December of 2018. Prior to joining Blackstone, Mr. Simon wasco-founder and Managing Director of Clarus, a venture capital firm focused on life sciences companies, since the firm’s inception in 2005. Prior to Clarus, Mr. Simon was a general partner at MPM Capital, Inc., a healthcare venture capital firm. He has more than 20 years of operating and investment experience in the biopharmaceutical industry including serving as vice president of business and corporate development at Genentech from 1989 to 2000. In addition to Gritstone, Mr. Simon is currently a member of the board of directors of Nuvelution Pharma, Inc., a public pharmaceutical company, and of Lycera Corp., a private pharmaceutical company, as well as chairman of the board of Sientra, Inc., a public medical aesthetics company. He has also been a member of the board of directors of numerous private and public life sciences companies including Achillion Pharmaceuticals, Inc., Avanir Pharmaceuticals, Inc., Barrier Therapeutics, Inc., Biovitrum AB, CoTherix, Inc., InterMune, Inc., Pearl Therapeutics Inc., QuatRx Pharmaceuticals Co., Rigel Pharmaceuticals, Inc., and Sangstat Medical Corporation. Mr. Simon is also a trustee at the Gladstone Institute, a privatenot-for-profit research institute affiliated with the University of California, San Francisco. Mr. Simon received a B.S. in microbiology from the University of Maryland and an M.B.A. from Loyola University. We believe that Mr. Simon is qualified to serve on our board of directors due to his experience as a board member of biotechnology and pharmaceutical companies, and his experience as an investor in new life sciences companies.

Peter Svennilson has served as a member of our board of directors since September 2015. In February 2007, Mr. Svennilson founded The Column Group, LP, or The Column Group, a San Francisco-based biotechnology venture capital firm, and currently serves as its managing partner. Mr. Svennilson also currently serves as a member of the board of two other public companies, NGM Biopharmaceuticals, Inc. and Constellation Pharmaceuticals. In addition, Mr. Svennilson serves on the board of ORIC Pharmaceuticals, Inc., a private biotechnology company. Previously, he served as chairman of the board of Seragon from January 2008 until it was acquired by Genentech in August 2014. He was the chairman of the board of Aragon from May 2009 until it was acquired by Johnson & Johnson in August 2013. Mr. Svennilson was also a board member of Ribon Therapeutics, Inc., a private biotechnology company from 2017 to 2019, Immune Design Corp., from 2014 until 2018, and PTC Therapeutics, Inc. from 2012 until 2014. Prior to founding The Column Group, he founded Three Crowns Capital, where he served as its managing partner from June 1996 to February 2007. From 1996 to 2006, Mr. Svennilson served as a board member of multiple biotechnology companies, including Rosetta Inpharmatics LLC, ChemoCentryx, Inc. and Somalogic, Inc. Prior to founding Three Crowns Capital, from 1987 to 1993 he was the associate managing director in charge of European Investment Banking Origination at Nomura Securities in London. Mr. Svennilson is currently a trustee for the Institute for Advanced Study in Princeton, New Jersey. Mr. Svennilson received an M.B.A. from the Stockholm School of Economics and Finance. We believe that Mr. Svennilson is qualified to serve on our board of directors due to his experience in the venture capital industry and in serving as a director of other public life science companies.

Thomas Woiwode, Ph.D. has served as a member of our board of directors since September 2015. Dr. Woiwode has been with Versant Venture Management, LLC, or Versant Ventures, a healthcare investment firm, since 2002 in various capacities, serving as a managing director since July 2014 and previously as a venture partner from June 2011 to July 2014. He has also served in a number of operating roles over this time, most recently as the chief operating officer of Okairos AG, or Okairos, a biopharmaceutical company developing genetic vaccines for major infectious diseases, from April 2011 until May 2013. Prior to Okairos, Dr. Woiwodeco-founded EuroVentures, a wholly owned biotechnology incubator within Versant Ventures, and in this role, served as the founding chief business officer for three biotechnology companies created within Versant Ventures. Before joining Versant Ventures, Dr. Woiwode also served as a research scientist at XenoPort, Inc. Dr. Woiwode currently serves

on the board of directors of CRISPR Therapeutics AG and Adverum Biotechnologies, Inc., and served on the board of directors of Audentes Therapeutics, Inc. from July 2013 to July 2017. Dr. Woiwode also serves on the board of directors of several private companies. Dr. Woiwode holds a B.A. in English and a B.S. in Chemistry from the University of California, Berkeley and a Ph.D. in Organic Chemistry as an NSF Fellow from Stanford University. We believe that Dr. Woiwode is qualified to serve on our board of directors due to his educational background, his experience as a board member and senior executive of biotechnology and pharmaceutical companies, and his experience as an investor in new life sciences companies.

Executive Officers

The executive officers of Gritstone are set forth below with their ages as of March 31, 2019:

Executive Officers

The following biographical information is furnished with regard to our executive officers (except for Dr. Allen, whose biographical information appears above under “Directors”) as of March 31, 2019:

Jean-Marc Bellemin has served as our Executive Vice President of Finance and Chief Financial Officer since January 2018. Prior to Gritstone, from January 2008 to December 2017, Mr. Bellemin served as senior vice president, market access, business solutions and services of Actelion Pharmaceuticals US Inc., or Actelion, a biotechnology company, until Actelion was acquired by Johnson & Johnson in 2017. Prior to Actelion, Mr. Bellemin held several financial leadership roles at Guerbet Group. Mr. Bellemin received a university degree in economics, a master’s degree in finance from Université Paris Dauphine, a postgraduate degree in finance and accounting from Université Paris IIPanthéon-Assas and an M.B.A. from the ESSEC Business School in Paris, France.

Matthew Hawryluk, Ph.D. has served as our Executive Vice President and Chief Business Officer since November 2015. Prior to Gritstone, from April 2011 to October 2015, Dr. Hawryluk held positions of increasing responsibility at Foundation Medicine, Inc., or Foundation Medicine, a public molecular diagnostics company, most recently serving as vice president, corporate and business development. Previously, he held roles in business development, marketing and product management across multiple divisions of Thermo Fisher Scientific, Inc. Dr. Hawryluk received a B.S. from the University of Notre Dame, a Ph.D. in cell biology and protein biochemistry from the University of Pittsburgh School of Medicine and an M.B.A. at Carnegie Mellon University’s Tepper School of Business as a Swartz Entrepreneurial Fellow.

Erin Jones has served as our Executive Vice President, Global Head of Regulatory Affairs and Quality Assurance since May 2016. Prior to Gritstone, from July 2014 to April 2016, Mr. Jones served as vice president, global head of regulatory affairs, medical writing, pharmacology and toxicology at Puma Biotechnology, Inc., or Puma, a public biopharmaceutical company. Prior to Puma, Mr. Jones served as director, regulatory affairs at BioMarin Pharmaceutical Inc. from July 2012 to July 2014. Earlier in his career, Mr. Jones held various positions at Genentech, Inc., or Genentech, a biotechnology corporation and subsidiary of Roche, including head of regulatory intelligence and leader of the HER Franchise Regulatory Group. Mr. Jones received a B.S. in microbiology and chemistry from the University of Pittsburgh and an M.S. in computer systems from Pennsylvania State University.

Karin Jooss, Ph.D. has served as our Executive Vice President of Research and Chief Scientific Officer since April 2016. Prior to Gritstone, from May 2009 to April 2016, Dr. Jooss served as head of cancer immuno-therapeutics in the vaccine immuno-therapeutics department at Pfizer, Inc., or Pfizer, a public pharmaceutical company, where she was also a member of the vaccine immuno-therapeutics leadership team and served as head of the immuno-pharmacology team. Prior to joining Pfizer, Dr. Jooss served as vice president of research at Cell Genesys, Inc., or Cell Genesys, from June 2005 to April 2009, and as senior director of research at Cell Genesys from July 2001 to June 2005. She is on the editorial board of Molecular Therapy and the Journal of Gene Medicine and is a member of the Immunology and Educational Committee of the American Society of Gene & Cell Therapy and the Industry Task Force of the Society for Immunotherapy of Cancer. Dr. Jooss has served on the board of directors of Fate Therapeutics, Inc., a publicly traded biopharmaceutical company, since March 2019. Dr. Jooss received her diploma in theoretical medicine from the University of Marburg in Germany, a Ph.D. in molecular biology and immunology from the University of Marburg in Germany and performed postgraduate work in gene therapy and immunology at the University of Pennsylvania.

Raphaël Rousseau, M.D., Ph.D.has served as our Executive Vice President, Chief Medical Officer since April 2017. Prior to Gritstone, from July 2012 to March 2017, Dr. Rousseau served as senior group medical director and global franchise head, pediatrics of Genentech. Before Genentech, Dr. Rousseau was senior medical director and lead of the pediatric global development team at Roche from October 2010 to June 2012, and international medical leader, hematology, at Roche from January 2009 to September 2010. Before joining Roche, Dr. Rousseau was a professor of medical and pediatric oncology at the Université Claude Bernard in Lyon, France. At the Léon Bérard Comprehensive Cancer Center in Lyon, Dr. Rousseau was head of the pediatric translational research program. Earlier in his career, he was a clinical fellow at Texas Children’s Cancer Center and a research fellow at the Center for Cell and Gene Therapy at Baylor College of Medicine in Houston. He received a Ph.D. in therapeutic biotechnologies at the Université Denis Diderot and an M.D. from Université René Descartes, both in Paris. He is board certified in pediatrics and has asub-specialty certification in pediatric hematology-oncology.

Roman Yelensky, Ph.D. has served as our Executive Vice President, Chief Technology Officer since March 2017. He joined Gritstone at its inception in October 2015 as executive vice president of sequencing and bioinformatics. Prior to Gritstone, from July 2010 to September 2015, Dr. Yelensky served as vice president of biomarker and companion diagnostic development at Foundation Medicine. Prior to Foundation Medicine, Dr. Yelensky was a senior scientist in biomarker development at Novartis AG from April 2009 to July 2010. He received a B.A. in computer science from Cornell University, an M.S. in computer science from Stanford University and a Ph.D. in bioinformatics and integrative genomics from theHarvard-MIT Division of Health Sciences and Technology.

Corporate Governance

Code of Business Conduct and Ethics

We have adopted a code of business conduct and ethics that applies to all of our employees, officers and directors, including those officers responsible for financial reporting. The code of business conduct and ethics is available on our website at http://www.gritstoneoncology.com. Any amendments to the code, or any waivers of its requirements, will be disclosed on our website.

Audit Committee and Audit Committee Financial Expert

We have a separately designated standing audit committee. The current members of our audit committee are Messrs. Krognes, Simon and Svennilson. Mr. Krognes serves as the chairperson of the committee. All members of our audit committee meet the requirements for financial literacy under the applicable rules and regulations of the SEC and Nasdaq. Our board of directors has determined that Mr. Krognes is an audit committee financial expert as defined under the applicable rules of the SEC and has the requisite financial sophistication as defined under the applicable rules and regulations of Nasdaq. Under the rules of the SEC, members of the audit committee must also meet heightened independence standards. Our board of directors has determined that each of the members of our audit committee are independent under the applicable rules of the SEC and Nasdaq. The audit committee operates under a written charter that satisfies the applicable standards of the SEC and Nasdaq.

Section 16(a) Beneficial Ownership Reporting Compliance

Section 16(a) of the Exchange Act requires the Company’s directors and executive officers, and persons who own more than 10% of a registered class of the Company’s equity securities, to file with the SEC initial reports of ownership and reports of changes in ownership of common stock and other equity securities of the Company. Officers, directors and greater than 10% stockholders are required by SEC regulations to furnish the Company with copies of all Section 16(a) forms they file.

To the Company’s knowledge, based solely on a review of the copies of such reports furnished to the Company and written representations that no other reports were required, the Company believes that all Section 16(a) filing requirements applicable to our officers, directors and greater than 10% beneficial owners were complied with during the year ended December 31, 2018.

ITEM 11. EXECUTIVE COMPENSATION.

This section discusses the material components of the executive compensation program for our “named executive officers” in the “Summary Compensation Table” below. In 2018, our named executive officers and their positions were as follows:

Dr. Aphale ceased serving as our Executive Vice President of Technical Operations and began serving as a Special Advisor to the Chief Executive Officer on December 7, 2018. Dr. Aphale terminated employment with us on March 12, 2019. As an “emerging growth company” as defined in the JOBS Act, we are not required to include a Compensation Discussion and Analysis section and have elected to comply with the scaled disclosure requirements applicable to emerging growth companies.

Summary Compensation Table

The following table provides information regarding the compensation of our named executive officers during the years ended December 31, 2018 and 2017.

Outstanding Equity Awards at FiscalYear-End 2018

The following table provides information regarding equity awards held by our named executive officers as of December 31, 2018.

Narrative to Summary Compensation Table and Outstanding Equity Awards at 2018 Fiscal Year End

2018 Salaries

Our named executive officers each receive a base salary to compensate them for services rendered to our company. The base salary payable to each named executive officer is intended to provide a fixed component of compensation reflecting the executive’s skill set, experience, role and responsibilities.

For fiscal year 2018, Dr. Allen’s annual base salary was $500,000, Mr. Bellemin’s base salary was $365,000, Dr. Aphale’s base salary was $340,000 and Dr. Yelensky’s base salary was $350,000. The annual base salaries of Dr. Allen and Dr. Yelensky were increased 14% and 17%, respectively as compared to their 2017 salaries.

2018 Bonuses

We maintain an annual performance-based cash bonus program in which each of our named executive officers participated in 2018. Each named executive officer’s target bonus is expressed as a percentage of base salary which can be achieved by meeting certain corporate goals established by the board of directors. The 2018 annual bonuses for Dr. Allen, Mr. Bellemin, Dr. Aphale and Dr. Yelensky were targeted at 50%, 35%, 35% and 35% of their respective base salaries.

In early 2019, the board of directors reviewed and approved the achievement of our 2018 corporate goals at 105.25%. Based on this level of achievement, our named executive officers were paid bonuses at 105.25% of their targeted amounts, except for Dr. Aphale, whose bonus was paid at 100% pursuant to the Transition and Separation Agreement entered into between us and Dr. Aphale. For additional details, see the description of the Transition and Separation Agreement below under the heading “Transition and Separation Agreement”.

The annual cash bonuses paid to each named executive officer for 2018 performance are set forth above in the Summary Compensation Table in the column titled“Non-Equity Incentive Plan Compensation.”

2018 Equity Compensation

On August 7, 2018, our board of directors granted Dr. Allen, Mr. Bellemin, Dr. Yelensky and Dr. Aphale an option to purchase 142,028, 51,448, 72,463 and 19,564 shares of our common stock, respectively (on a split-adjusted basis). Each option had an exercise price per share equal to $9.59, which was the fair market value of our common stock on the date of grant (on a split-adjusted basis), as determined by our board of directors. The options were intended to incentivize our named executive officers to complete the initial public offering of our common stock and did not commence vesting until September 27, 2018, the effective date of the registration statement for the initial public offering of our common stock. Each option vests as to 1/48^th of the initial number of shares underlying the option on each monthly anniversary of September 27, 2018, subject to the named executive officer’s continued service to us.

Also on August 7, 2018, in accordance with his offer letter with us dated February 2018, the board of directors granted Dr. Aphale an option to purchase 72,463 shares of our common stock (on a split-adjusted basis) pursuant to our 2015 Equity Incentive Plan. The option has an exercise price per share of $9.59, which was the fair market value of our common stock on the date of grant (on a split-adjusted basis), as determined by our board of directors. The option was scheduled to vest as to 25% of the initial shares underlying the option on the first anniversary of Dr. Aphale’s commencement of employment with us (March 12, 2018) and as to 1/48^th of the initial shares underlying the option on each monthly anniversary of his commencement date thereafter. Dr. Aphale terminated employment with us on March 12, 2019 after 25% of the shares underlying the option had vested. The unvested portion of each of his options was forfeited upon his termination of employment. For additional details, see the description of the Transition and Separation Agreement below under the heading “Transition and Separation Agreement”.

In February 2018, in accordance with his offer letter with us dated December 2017, the board of directors granted Mr. Bellemin an option to purchase 166,542 shares of our common stock (on a split-adjusted basis) pursuant to our 2015 Equity Incentive Plan. Mr. Bellemin’s option grant vests as to 25% of the shares initially underlying the option on the first anniversary of Mr. Bellemin’s employment commencement date (January 5, 2018), and as to 1/48th of the shares initially underlying the option on each monthly anniversary thereafter, subject to Mr. Bellemin’s continued service to the Company on each applicable vesting date.

Options granted to Dr. Allen, Mr. Bellemin and Dr. Yelensky are subject to the accelerated vesting provisions in their employment agreements described below under “Executive Compensation Arrangements.”

In connection with our IPO, we adopted our 2018 Incentive Award Plan, referred to below as the 2018 Plan, in order to facilitate the grant of cash and equity incentives to directors, employees (including our named executive officers) and consultants of our company and certain of its affiliates and to enable us to obtain and retain services of these individuals, which is essential to our long-term success. The 2018 Plan became effective on the day prior to the first public trading date of our common stock, and since then no further grants have been or will be made under our 2015 Equity Incentive Plan.

Executive Compensation Arrangements

Employment Agreements

In September 2018, we entered into new employment agreements with each of our named executive officers, which superseded in their entirety their prior offer letters with us. Each employment agreement provides that the executive’s employment with us isat-will, and provides for an annual base salary and target annual bonus (expressed as a percentage of base salary), as well as severance and change in control benefits, as described below.

Under Dr. Allen’s employment agreement, if he is terminated without “cause” or resigns for “good reason” (as each is defined in his employment agreement), he will be eligible to receive the following: (i) an amount equal to the sum of his base salary and target annual bonus; and (ii) payment or reimbursement of up to 12 months of healthcare continuation coverage. In addition, if Dr. Allen is terminated without cause or resigns for good reason during the period commencing three months before and ending 12 months after a change in control of the Company, he will be eligible to receive the following: (i) an amount equal to the sum of (A) 150% of his base salary and (B) his target annual bonus; (ii) payment or reimbursement of up to 18 months of healthcare continuation coverage; and (iii) full vesting acceleration of all then-outstanding equity awards. The foregoing severance benefits are subject to Dr. Allen’s execution andnon-revocation of a general release of claims against the Company.

Under each of Mr. Bellemin’s and Dr. Yelensky’s employment agreements, if either is terminated without “cause” or resigns for “good reason” (as each is defined in the employment agreement), he will be eligible to receive the following: (i) an amount equal to the sum of (A) 75% of his base salary and (B) his target annual bonus; and (ii) payment or reimbursement of up to nine months of healthcare continuation coverage. In addition, if either is terminated without cause or resigns for good reason during the period commencing three months before and ending 12 months after a change in control of the Company, he will be eligible to receive the following: (i) an amount equal to the sum of his base salary and target annual bonus; (ii) payment or reimbursement of up to 12 months of healthcare continuation coverage; and (iii) full vesting acceleration of all then-outstanding equity awards. The foregoing severance benefits are subject to the executive’s execution andnon-revocation of a general release of claims against the Company.

Transition and Separation Agreement

In connection with his transition from serving as our Executive Vice President of Technical Operations to the role as Special Advisor to the Chief Executive Officer on December 7, 2018 and the termination of his employment with us on March 12, 2019, we entered into a Transition and Separation Agreement with Dr. Aphale. Under the Transition and Separation Agreement, Dr. Aphale’s bonus for 2018 was fixed at 100% of his target bonus amount, we continued to pay his base salary and he continued to be eligible for benefits under our plans through his termination date. Pursuant to the Transition and Separation Agreement, in connection with the termination of his employment on March 12, 2019, and in exchange for a release of claims against the Company, he received (i) cash severance of $374,000 (an amount equal to nine months of his base salary and his target bonus) and (ii) payment or reimbursement of up to nine months of healthcare continuation coverage.

Other Elements of Compensation

Retirement Savings and Health and Welfare Benefits

We maintain a 401(k) retirement savings plan for our employees, including our named executive officers, who satisfy certain eligibility requirements. Our named executive officers are eligible to participate in the 401(k) plan on the same terms as other full-time employees. Currently, we may match (in our discretion) contributions made by participants in the 401(k) plan in the amount equal to 50% of up to 4% of the participant’s eligible compensation contributed to the plan, not to exceed 2% of a participant’s eligible compensation. We believe that providing a vehicle fortax-deferred retirement savings though our 401(k) plan adds to the overall desirability of our executive compensation package and further incentivizes our employees, including our named executive officers, in accordance with our compensation policies.

All of our full-time employees, including our named executive officers, are eligible to participate in our health and welfare plans, including medical, dental and vision benefits; medical and dependent care flexible spending accounts; short-term and long-term disability insurance; and life and AD&D insurance.

Perquisites and Other Personal Benefits

We provide limited perquisites to our named executive officers when our compensation committee determines that such perquisites are necessary or advisable to fairly compensate or incentivize our employees. In 2018 we reimbursed relocation expenses for Dr. Aphale’s relocation to our headquarters as well as reimbursement of taxes incurred in connection with such relocation expenses.

Director Compensation

Pursuant to the Director Compensation Program, which we adopted in connection with our IPO, ournon-employee directors receive cash compensation as follows:

Under the Director Compensation Program, eachnon-employee director will automatically be granted an option to purchase 15,942 shares of our common stock upon the director’s initial appointment or election to our board of directors, referred to as the Initial Grant, and an option to purchase 7,971 shares of our common stock automatically on the date of each annual stockholder’s meeting thereafter, referred to as the Annual Grant. The Initial Grant will vest in substantially equal monthly installments for three years from the date of grant, subject to continued service through each applicable vesting date. The Annual Grant will vest on the earlier of the first anniversary of the date of grant or the date of the next annual stockholder’s meeting to the extent unvested as of such date, subject to continued service through each applicable vesting date. In February 2019, our board of directors amended the Director Compensation Program to increase the number of shares underlying the Annual Grant to 8,570. All other terms of the Director Compensation Program remain unchanged.

On August 7, 2018, in connection with Steve Krognes’ appointment to our board of directors the preceding month, we granted Mr. Krognes an option to purchase 15,942 shares of our common stock. The option has an exercise per share of $9.59 and vests in equal monthly installments over 4 years.

Director Compensation Table

The following table sets forth information regarding compensation earned by or paid to ournon-employee directors during 2018:

Compensation Committee Interlocks and Insider Participation

During the year ended December 31, 2018, Thomas Woiwode, Ph.D., Richard Heyman, Ph.D., Steve Krognes and Patrick Mahaffy (a former member of our board of directors) served as members of our compensation committee. None of the members of our compensation committee during 2018 nor any of the current members of the committee has at any time been one of our officers or employees. None of our executive officers currently serves, or in the past fiscal year has served, as a member of the board of directors or compensation committee of any entity that has one or more executive officers on our board of directors or compensation committee.

ITEM 12. SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT AND RELATED STOCKHOLDER MATTERS.

The following table presents information as to the beneficial ownership of our common stock as of March 31, 2019 for:

Beneficial ownership is determined in accordance with the rules of the SEC and generally includes voting or investment power with respect to securities. Unless otherwise indicated below, to our knowledge, the persons and entities named in the table have sole voting and sole investment power with respect to all shares beneficially owned, subject to community property laws where applicable. Shares of our common stock subject to options that are currently exercisable or exercisable within 60 days of March 31, 2019 are deemed to be outstanding and to be beneficially owned by the person holding the options for the purpose of computing the percentage ownership of that person, but are not treated as outstanding for the purpose of computing the percentage ownership of any other person.

The percentage of shares beneficially owned is computed on the basis of 29,196,656 shares of our common stock outstanding as of March 31, 2019. This table is based upon information supplied by officers, directors and principal stockholders and Schedules 13D and Schedules 13G, if any, filed with the SEC, as well as information provided by The Nasdaq Stock Market, LLC. Unless otherwise indicated, the address of each of the individuals and entities named below is c/o Gritstone Oncology, Inc., 5858 Horton Street, Suite 210, Emeryville, CA 94608.

Equity Compensation Plan Information

The following table provides certain information as of December 31, 2018, with respect to all of our equity compensation plans in effect on that date:

ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS, AND DIRECTOR INDEPENDENCE.

Certain Relationships and Related Transactions

The following is a description of transactions since January 1, 2018 to which we have been a party, in which the amount involved exceeds $120,000, and in which any of our directors, executive officers or beneficial owners of more than 5% of our capital stock, or an affiliate or immediate family member thereof, had or will have a direct or indirect material interest.

Sales and Purchases of Securities

Series C Convertible Preferred Stock Financing

In June, July and August 2018, we issued an aggregate of 1,611,603 shares of our Series C convertible preferred stock at a price per share of $13.04 (in each case, after giving effect to the1-for-6.9 reverse stock split of our outstanding capital stock we effected on September 20, 2018) for aggregate proceeds to us of approximately $21.0 million. Of these shares, we sold 153,360 shares of Series C convertible preferred stock to entities affiliated with Redmile Group, which beneficially owned more than 5% of our capital stock immediately prior to and following the transaction.

Participation in IPO

Certain of our stockholders, including entities affiliated with certain of our directors, purchased, and we directed allocations for, an aggregate of approximately $31.0 million of shares of our common stock in our initial public offering at the public offering price and on the same terms as the other purchasers in this offering and not pursuant to anypre-existing contractual rights or obligations.

Director and Executive Officer Compensation

See “Executive Compensation” and “Director Compensation” for information regarding compensation of directors and executive officers.

Employment Agreements

We have entered into employment agreements with our executive officers. For more information regarding these agreements, see “Executive Compensation — Narrative to Summary Compensation Table and Outstanding Equity Awards at 2018 Fiscal Year End.”

Investors’ Rights Agreement

We entered into an amended and restated investors’ rights agreement with the purchasers of our outstanding preferred stock and certain of our other stockholders, including entities with which certain of our directors are affiliated. As of December 31, 2018, the holders of approximately 19.4 million shares of our common stock are entitled to rights with respect to the registration of their shares under the Securities Act.

Indemnification Agreements and Directors’ and Officers’ Liability Insurance

We have entered into indemnification agreements with each of our directors and executive officers. These agreements require us to, among other things, indemnify each director and executive officer to the fullest extent permitted by Delaware law, including indemnification of expenses such as attorneys’ fees, judgments, penalties fines and settlement amounts incurred by the director or executive officer in any action or proceeding, including any action or proceeding by or in right of us, arising out of the person’s services as a director or executive officer. We have obtained an insurance policy that insures our directors and executive officers against certain liabilities, including liabilities arising under applicable securities laws.

Policies and Procedures for Related Party Transactions

Our board of directors has adopted a written related person transaction policy setting forth the policies and procedures for the review and approval or ratification of related person transactions. This policy covers, with certain exceptions set forth in Item 404 ofRegulation S-K under the Securities Act, any transaction, arrangement or relationship, or any series of similar transactions, arrangements or relationships in which we were or are to be a participant, where the amount involved exceeds $120,000 and a related person had or will have a direct or indirect material interest, including without limitation purchases of goods or services by or from the related person or entities in which the related person has a material interest, indebtedness, guarantees of indebtedness and employment by us of a related person. In reviewing and approving any such transactions, our audit committee is tasked to consider all relevant facts and circumstances, including but not limited to whether the transaction is on terms comparable to those that could be obtained in an arm’s length transaction with an unrelated third party and the extent of the related person’s interest in the transaction. All of the transactions described in this section occurred prior to the adoption of this policy.

Director Independence

As required under the Nasdaq Global Select Market (“Nasdaq”) rules and regulations, a majority of the members of a listed company’s board of directors must qualify as “independent,” as affirmatively determined by such board. The board of directors consults with the Company’s counsel to ensure that the board of directors’ determinations are consistent with all relevant securities and other laws and regulations regarding the definition of “independent,” including those set forth in pertinent Nasdaq listing standards, as in effect from time to time.

Consistent with these considerations, our board of directors has determined that all of our directors, other than Dr. Allen, qualify as “independent” directors in accordance with the Nasdaq listing requirements. Dr. Allen is not considered independent because he is an employee of Gritstone. The Nasdaq independence definition includes a series of objective tests, such as that the director is not, and has not been for at least three years, one of our employees and that neither the director nor any of his or her family members has engaged in various types of business dealings with us. In addition, as required by Nasdaq rules, our board of directors has made a subjective determination as to each independent director that no relationships exist, which, in the opinion of our board of directors, would interfere with the exercise of independent judgment in carrying out the responsibilities of a director. In making these determinations, our board of directors considered information provided by the directors and us with regard to each director’s business and personal activities and relationships as they may relate to us and our management. There are no family relationships among any of our directors or executive officers.

As required under Nasdaq rules and regulations, our independent directors meet in regularly scheduled executive sessions at which only independent directors are present. All of the committees of our board of directors are comprised entirely of directors determined by the board of directors to be independent within the meaning of Nasdaq and SEC rules and regulations applicable to the members of such committees.

ITEM 14. PRINCIPAL ACCOUNTING FEES AND SERVICES.

The following table provides information regarding the fees incurred to Ernst & Young LLP (“EY”) during the years ended December 31, 2018 and 2017. The audit committee approved all of the fees described below incurred since our initial public offering (“IPO”) in October 2018.

Pre-Approval Policies and Procedures

The audit committee or a delegate of the audit committeepre-approves, or provides pursuant topre-approvals policies and procedures for thepre-approval of, all audit andnon-audit services provided by its independent registered public accounting firm. This policy is set forth in the charter of the audit committee and is available at http://www.gritstoneoncology.com.

The audit committee approved all of the audit, audit-related, tax and other services provided by EY for 2017 and all of the audit, audit-related, tax and other services provided by EY in 2018 following our IPO in October 2018 and, in each case, the estimated costs of those services. Actual amounts billed, to the extent in excess of the estimated amounts, are periodically reviewed and approved by the audit committee.

PART IV

ITEM

Item 15. EXHIBITS, FINANCIAL STATEMENT SCHEDULES.

(a)    The following documents were filed as part of the Original Filing:

1.    Financial Statements. The financial statements of Gritstone Oncology, Inc. included in Part II, Item 8 of the Original Filing.

2.Exhibits and Financial Statement Schedules. All schedules were omitted from the Original Filing because they were not applicable or the required information was shown in the financial statements or notes thereto.

3.    Exhibits.

(a)(3) Exhibits

The exhibitsdocuments listed on the Exhibit Index of the Original Filing.

(b)The exhibit list in the Exhibit Index immediately preceding the signature pageare filed with this report, in each case as indicated therein (numbered in accordance with Item 601 of this Amendment are being filed as part of this Amendment.Regulation S-K).

SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this Annual Report on Form10-K/A to be signed on its behalf by the undersigned, thereunto duly authorized.

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, this Annual Report on Form 10-K/A has been signed below by the following persons on behalf of the Registrant in the capacities and on the dates indicated.