September 20, 2018

Andrew Allen, M.D., Ph.D.
President and Chief Executive Officer
Gritstone Oncology, Inc.
5858 Horton Street, Suite 210
Emeryville, CA 94608

       Re: Gritstone Oncology, Inc.
           Amendment No. 1 to Registration Statement on Form S-1
           Filed September 17, 2018
           File No. 333-226976

Dear Dr. Allen:

      We have reviewed your amended registration statement and have the
following
comments. In some of our comments, we may ask you to provide us with
information so we
may better understand your disclosure.

       Please respond to this letter by amending your registration statement
and providing the
requested information. If you do not believe our comments apply to your facts
and
circumstances or do not believe an amendment is appropriate, please tell us why
in your
response.

       After reviewing any amendment to your registration statement and the
information you
provide in response to these comments, we may have additional comments.

Amendment No. 1 to Registration Statement on Form S-1

Use of Proceeds, page 73

1.     We refer to your response to comment 3 of our letter dated June 3, 2018.
Please revise
       your disclosure to indicate what the continued buildout of your
manufacturing facility
       entails and what you expect to accomplish regarding the buildout using
the proceeds from
       the offering.
Capitalization, page 76

2.     You disclose here and throughout your filing that you assume the
automatic conversion of
       your convertible preferred stock into common stock immediately prior to
the
 Andrew Allen, M.D., Ph.D.
Gritstone Oncology, Inc.
September 20, 2018
Page 2
      consummation of your offering. It appears that you may not meet the
offering price
      criterion identified in Note 8 to your Unaudited Interim Condensed
Financial Statements
      on page F-52. Please represent to us and revise your disclosure
accordingly that in the
      event this criterion is not met that you will receive the affirmative
election of at least a
      majority of your convertible preferred stockholders to effect conversion.
       You may contact Rolf Sundwall at 202-551-3105 or Jim B. Rosenberg at
202-551-3679 if
you have questions regarding comments on the financial statements and related
matters. Please
contact Ada D. Sarmento at 202-551-3798 or Mary Beth Breslin at 202-551-3625
with any other
questions.



                                                             Sincerely,
FirstName LastNameAndrew Allen, M.D., Ph.D.
                                                             Division of
Corporation Finance
Comapany NameGritstone Oncology, Inc.
                                                             Office of
Healthcare & Insurance
September 20, 2018 Page 2
cc:       Brian J. Cuneo, Esq.
FirstName LastName