March 14, 2018

Thomas Gad
Founder, Chairman, President and Head of Business Development
Y-mAbs Therapeutics, Inc.
750 Third Avenue
9th Floor
New York, NY 10017

       Re: Y-mAbs Therapeutics, Inc.
           Draft Registration Statement on Form S-1
           Submitted February 13, 2018
           CIK No. 0001722964

Dear Mr. Gad:

       We have reviewed your draft 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 providing the requested information and
either submitting
an amended draft registration statement or publicly filing your registration
statement on
EDGAR. 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 the information you provide in response to these comments
and your
amended draft registration statement or filed registration statement, we may
have additional
comments.

Draft Registration Statement on Form S-1

Table of Contents, page i

1.     We note your statements regarding market data used in the prospectus,
including that the
       sources of the information do not guarantee the accuracy or completeness
of the
       information and that investors are cautioned "not to give undue weight"
to estimates.
       Please revise these statements to eliminate any implication that
investors are not entitled
       to rely on the information included in your registration statement.
 Thomas Gad
FirstName LastNameThomas Gad
Y-mAbs Therapeutics, Inc.
Comapany2018
March 14, NameY-mAbs Therapeutics, Inc.
June 16, 2017 Page 2
Page 2
FirstName LastName
Summary, page 1

2.       Please disclose any active INDs related to your product candidates,
the date of filing for
         each IND, the sponsor, the subject matter and the status of the IND.
Please include similar
         disclosure with respect to the EMA or any other drug regulatory
authorities.
Naxitamab Mechanism of Action, page 1

3.       We note your disclosure that you have not observed any
life-threatening side effects with
         naxitamab to date. Please disclose whether any patients have
experienced serious adverse
         events, what those events were and how many patients experienced them.
Implications of Being an Emerging Growth Company, page 7

4.       Please supplementally provide us with copies of all written
communications, as defined in
         Rule 405 under the Securities Act, that you, or anyone authorized to
do so on your behalf,
         present to potential investors in reliance on Section 5(d) of the
Securities Act, whether or
         not they retain copies of the communications.
Use of Proceeds, page 76

5.       We note your disclosure of the intended uses of proceeds in this
section. Please specify
         how far in the clinical development of your omburtamab-DTPA product
candidate and
         BsAb product candidates you expect to reach using proceeds from the
offering. If any
         material amounts of other funds are necessary to accomplish the
specified purposes for
         which the proceeds are to be obtained, state the amounts and sources
of such other funds
         needed for each such specified purpose and the sources thereof. Refer
to Instruction 3 to
         Item 504 of Regulation S-K.
Management's Discussion and Analysis of Financial Condition and Results of
Operations
Critical Accounting Policies and Significant Judgments and Estimates
Determination of the Fair Value of Common Stock, page 91

6.       Once you have an estimated offering price or range, please explain to
us how you
         determined the fair value of the common stock underlying your equity
issuances and the
         reasons for any differences between the recent valuations of your
common stock leading
         up to the initial public offering and the estimated offering price.
This information will help
         facilitate our review of your accounting for equity issuances
including stock compensation
         and beneficial conversion features.
Results of Operations
Research and Development Expenses, page 93

7.       Please expand your disclosure to quantify the total costs incurred
during each period
         presented for each project or product candidate separately to provide
more transparency as
 Thomas Gad
FirstName LastNameThomas Gad
Y-mAbs Therapeutics, Inc.
Comapany2018
March 14, NameY-mAbs Therapeutics, Inc.
June 16, 2017 Page 3
Page 3
FirstName LastName
         to the type of expenses incurred. If you cannot disaggregate the
amount of expense by
         product candidate, disaggregate the amount by nature of expenses or in
some other
         manner.
Business, page 100

8.       We note your disclosure that a single dose of 4mCi 124 I-omburtamab
was generally
         considered safe, treatment with 131 I-omburtamab was generally safe
and omburtamab
         has an acceptable safety profile. Please remove statements suggesting
that your product
         candidates are safe and effective as approval by the FDA and other
regulatory agencies is
         dependent on such agencies making this determination.
9.       Please define DLT, EFS, CR/VGPR and mCi the first time they are used
in this section.
Omburtamab Overview, page 117

10.      We note your disclosure that omburtamab has generally been well
tolerated in over 200
         patients treated over 14 years for multiple indications, with no
significant long-term
         toxicities. Please disclose whether any patients have experienced
serious adverse events,
         what those events were and how many patients experienced them.
131 I-omburtamab ... Clinical Development Program, page 119

11.      We note your disclosure that safety data for 131 I-omburtamab shows no
significant long-
         term toxicities for more than 200 patients from multiple clinical
trials including patients
         with other cancer types such as DIPG and DSRCT. Please disclose
whether any patients
         have experienced serious adverse events, what those events were and
how many patients
         experienced them.
Study 03-133: Phase I Study..., page 120

12.      We note your disclosure that 44 treatment-related serious adverse
events were observed in
         this trial, of which 36 were Grade 4, six were Grade 3 and two were
Grade 2. Please
         disclose how you define Grades 2, 3 and 4, what the serious adverse
events were in each
         grade and how many patients experienced them.
Intellectual Property
Patent Portfolio, page 138

13.      Please specify the expiration dates for the most significant patents
within each portfolio.
MSK Agreements, page 141

14.      We note that you have several agreements with Memorial Sloan-Kettering
Cancer Center,
         of which only the two license agreements will be filed as exhibits.
Please file
         the Sponsored Research Agreement, Master Data Services Agreement,
Investigator-
 Thomas Gad
Y-mAbs Therapeutics, Inc.
March 14, 2018
Page 4
      Sponsored Master Clinical Trial Agreement, and two Core Facility Service
Agreements or
      tell us why you believe that you are not required to file such agreements
pursuant to Item
      601(b)(10) of Regulation S-K.
Management, page 159

15.   Please disclose Dr. Lund-Hansen's business experience from 2013 to his
appointment as
      your Senior Vice President, Head of Technical Operations in 2016. Refer
to Item 401(e)
      of Regulation S-K.
Principal Stockholders, page 186

16.   Please revise your disclosure to identify the natural person or persons
who have voting
      and investment control of the shares held by entities in the table, such
as MSK and Peter
      Bang Holding ApS. Please also disclose the natural person or persons with
      whom Dr. Healy shares voting and dispositive power over the shares held
by Sofinnova
      Venture Partners X, L.P.
Description of Capital Stock, page 189

17.   We note your disclosure that the description of your capital stock is
qualified in its
      entirety by reference to the applicable provisions of the DGCL. It is not
appropriate to
      qualify your disclosure by reference to information that is not included
in the prospectus
      or filed as an exhibit to the registration statement. Please revise
accordingly.
General

18.   Please provide us proofs of all graphics, visual, or photographic
information you will
      provide in the printed prospectus prior to its use, for example in a
preliminary prospectus.
      Please note that we may have comments regarding this material.
       You may contact Rolf Sundwall at 202-551-3105 or Kevin Vaughn at
202-551-3494 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.


FirstName LastNameThomas Gad
                                                            Division of
Corporation Finance
Comapany NameY-mAbs Therapeutics, Inc.
                                                            Office of
Healthcare & Insurance
June 16, 2017 Page 4
cc: Dwight A. Kinsey
FirstName LastName