As filed with the Securities and Exchange Commission on March 11, 2020

Registration No. 333-            

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Gritstone Oncology, Inc.

(Exact name of Registrant as specified in its charter)

2018 Incentive Award Plan

2018 Employee Stock Purchase Plan

(Full Title of the Plan)

Andrew Allen, M.D., Ph.D.

President and Chief Executive Officer

Gritstone Oncology, Inc.

5959 Horton Street, Suite 300

Emeryville, California 94608

(510) 871-6100

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Alan C. Mendelson, Esq.

Brian J. Cuneo, Esq.

Latham & Watkins LLP

140 Scott Drive

Menlo Park, California 94025

Telephone: (650) 328-4600

Facsimile: (650) 463-2600

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a 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 Rule 12b-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 7(a)(2)(B) of the Securities Act. ☒

CALCULATION OF REGISTRATION FEE

Proposed sale to take place as soon after the effective date of the

registration statement as awards under the plans are exercised and/or vest.

REGISTRATION OF ADDITIONAL SECURITIES

By a registration statement on Form S-8 filed with the Securities and Exchange Commission (the “SEC”) on October 2, 2018 (File No. 333-227665) (the “Original Registration Statement”), Gritstone Oncology, Inc. (the “Registrant”) registered 2,782,920 shares of common stock, par value $0.0001 per share (the “Common Stock”), issuable under the Gritstone Oncology, Inc. 2018 Incentive Award Plan (the “2018 Plan”), and 282,334 shares of Common Stock issuable under the Gritstone Oncology, Inc. 2018 Employee Stock Purchase Plan (the “ESPP”). The Original Registration Statement also registered 2,355,270 shares of Common Stock issuable under the Gritstone Oncology, Inc. 2015 Equity Incentive Plan, as amended (the “2015 Plan”), which shares become available for issuance under the 2018 Plan to the extent awards under the 2015 Plan are forfeited or lapse unexercised and are not issued under the 2015 Plan. By a registration statement on Form S-8 filed with the SEC on March 28, 2019 (File No. 333-230581) (the “2019 Registration Statement”), the Registrant registered an additional 1,160,000 shares of Common Stock issuable under the 2018 Plan and an additional 290,000 shares of Common Stock issuable under the ESPP. The Registrant is hereby registering an additional 1,454,553 shares of Common Stock issuable under the 2018 Plan and an additional 363,638 shares of Common Stock issuable under the ESPP, which shares are now available for grant due to automatic annual increase provisions in the 2018 Plan and ESPP.

INCORPORATION BY REFERENCE OF CONTENTS OF

REGISTRATION STATEMENT ON FORM S-8

Pursuant to Instruction E of Form S-8, the contents of the Original Registration Statement and 2019 Registration Statement are incorporated by reference in this registration statement on Form S-8.

INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

The information called for in Part I of Form S-8 is not being filed with or included in this Form S-8 (by incorporation by reference or otherwise) in accordance with the rules and regulations of the SEC.

Item 8. Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the Registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the Emeryville, California, on this 11th day of March, 2020.

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below does hereby constitute and appoint Andrew Allen, M.D., Ph.D. and Jean-Marc Bellemin and each of them, with full power of substitution and full power to act without the other, his or her true and lawful attorney-in-fact and agent to act for him or her in his or her name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this registration statement, and to file this registration statement, with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in order to effectuate the same as fully, to all intents and purposes, as they or he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or any of them, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement has been signed by the following persons in the capacities and on the date indicated.

Exhibit 5.1

.

Gritstone Oncology, Inc.

5959 Horton Street, Suite 300

Emeryville, CA 94608

Ladies and Gentlemen:

We have acted as special counsel to Gritstone Oncology, Inc., a Delaware corporation (the “Company”), in connection with the registration by the Company of an aggregate of 1,818,191 shares of common stock of the Company, par value $0.0001 per share (the “Shares”), issuable under the Company’s 2018 Incentive Award Plan (the “2018 Plan”) and 2018 Employee Stock Purchase Plan (the “ESPP” and together with the 2018 Plan, the “Plans”).

The Shares are included in a registration statement on Form S-8 under the Securities Act of 1933, as amended (the “Act”), filed with the Securities and Exchange Commission (the “Commission”) on March 11, 2020 (the “Registration Statement”). This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement or the related prospectuses, other than as expressly stated herein with respect to the issuance of the Shares.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters. We are opining herein as to the General Corporation Law of the State of Delaware (the “DGCL”), and we express no opinion with respect to any other laws.

March 11, 2020

Page 2

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof, when the Shares shall have been duly registered on the books of the transfer agent and registrar therefor in the name or on behalf of the purchasers and have been issued by the Company against payment therefor in the circumstances contemplated by the Plans, assuming in each case that the individual issuances, grants or awards under the Plans are duly authorized by all necessary corporate action and duly issued, granted or awarded and exercised in accordance with the requirements of law and the applicable Plans (and the agreements and awards duly adopted thereunder and in accordance therewith), the issue and sale of the Shares will have been duly authorized by all necessary corporate action of the Company, and the Shares will be validly issued, fully paid and nonassessable. In rendering the foregoing opinion, we have assumed that the Company will comply with all applicable notice requirements regarding uncertificated shares provided in the DGCL.

This opinion is for your benefit in connection with the Registration Statement and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Act. We consent to your filing this opinion as an exhibit to the Registration Statement. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.

Very truly yours,

/s/ Latham & Watkins LLP

Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We consent to the incorporation by reference in the Registration Statement (Form S-8) pertaining to the 2018 Incentive Award Plan and 2018 Employee Stock Purchase Plan of Gritstone Oncology, Inc. of our report dated March 11, 2020, with respect to the financial statements of Gritstone Oncology, Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2019, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

Redwood City, California

March 11, 2020