July 8, 2019

Derek Maetzold
Chief Executive Officer
CASTLE BIOSCIENCES INC
820 S. Friendswood Drive, Suite 201
Friendswood, Texas 77546

       Re: CASTLE BIOSCIENCES INC
           Registration Statement on Form S-1
           Filed June 26, 2019
           File No. 333-232369

Dear Mr. Maetzold:

       We have reviewed your 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. Unless
we note
otherwise, our references to prior comments are to comments in our June 10,
2019 letter.

Registration Statement on Form S-1

Summary, page 1

1.     We partially reissue prior comment 2. Please update the amount of shares
outstanding and
       the amount of shares outstanding after the offering as of the same date
as the beneficial
       ownership table.
Use of Proceeds, page 55

2.     We partially reissue prior comment 4. We continue to note the disclosure
that while these
       are your current intentions regarding the use of proceeds, actual
expenditures may differ
       materially from the estimates described in this section. The company may
reserve the
       right to change the use of proceeds, provided that such reservation is
due to certain
 Derek Maetzold
CASTLE BIOSCIENCES INC
July 8, 2019
Page 2
      contingencies that are discussed specifically and the alternatives to
such use in that event
      are indicated. See Instruction 7 to Item 504 of Regulation S-K. Please
revise accordingly
2018 Loan and Security Agreement, page 73

3.    We note your response to prior comment 5 and the June 13, 2019 amendment
to the 2018
      Loan and Security Agreement which amended the terms of the trailing
revenue covenant.
      Given your prior disclosure regarding your projections that you may be
unable to maintain
      compliance with the revenue covenant during the next 12 months and your
historic
      revenue; please disclose your minimum revenue targets through December
2019 or tell us
      how you concluded that these targets are not material.
Description of Capital Stock, page 151

4.    We note your revisions in response to prior comment 6 regarding exclusive
forum. Please
      make conforming changes to your risk factor disclosure on pages 51 and
52. Also, please
      include disclosure on page 155 and in the risk factors regarding the
alternate courts that
      will be the appropriate forum if the Court of Chancery of the State of
Delaware lacks
      subject matter jurisdiction.
        We remind you that the company and its management are responsible for
the accuracy
and adequacy of their disclosures, notwithstanding any review, comments, action
or absence of
action by the staff.

       Refer to Rules 460 and 461 regarding requests for acceleration. Please
allow adequate
time for us to review any amendment prior to the requested effective date of
the registration
statement.

      You may contact Ruairi Regan at 202-551-3269 or Pamela Howell, Special
Counsel, at
202-551-3357 with any questions.



                                                            Sincerely,

FirstName LastNameDerek Maetzold                            Division of
Corporation Finance
                                                            Office of
Beverages, Apparel and
Comapany NameCASTLE BIOSCIENCES INC
                                                            Mining
July 8, 2019 Page 2
cc:       Karen Anderson, Esq.
FirstName LastName