SecProbe.io

July 22 , 2013

Via E -mail
Ramesh Kumar, Ph.D.
President and Chief Executive Officer
Onconova Therapeutics, Inc.
375 Pheasant Run
Newtown, PA 18940

Re: Onconova Therapeutics, Inc.
Amendment No. 2  to Registration Statement on Form S -1
Filed July 18 , 2013
File No. 333 -189358

Dear Dr. Kumar:

We have reviewed your amended registration statement and correspondence dated July
17, 2013 and have  the following comments. In some of our comments, we may ask you to
provide us with infor mation so we may better understand your disclosure.

Please respond to this letter by providing the requested infor mation and amending
your registration statement.  If  you do  not believe our comments apply to your facts and
circu mstances or do not believe an  amendment is a ppropriate, please tell us why in your
response.

After revie wing the infor mation you provide  in response to these com ments and your
amended registrat ion state ment, we may have additio nal co mments.

Exhibit 5.1

1. We note counsel’s opinion that the securities will be validly issued, fully paid and
non-assessable is subject to the assumption that the Tenth Amended and Restated
Certificate of Incorporation will be filed with the Secretary of State of the State of
Delaware .  Please either file a revised legal opinion to remove this assumption or
confirm that an appropriately unqualified opinion will be f iled by post -effective
amendment no later than the closing date of the offering.  See Sections II.B.2.f. and
II.B.3.a. of Staff Legal Bulletin No. 19.

2. Please also provide a revised legal opinion to modify the statement regarding “the
legal power and authority of all persons signing on behalf of parties to all

Ramesh Kumar , Ph.D.
Onconova Therapeutics, Inc.
July 22 , 2013
Page 2

 documents,” to limit this qualification to persons signing on behalf of parties other
than the r egistrant.

We urge all persons who are responsible for the accuracy and adequacy of the disclosure
in the filing to be certain that the filing includes the information the Securities Act of 1933 and
all applicable Securities Act rules require. Since the  company and its management are in
possession of all facts relating to a company’s disclosure, they are responsible for the accuracy
and adequacy of the disclosures they have made.

Please contact Austin Stephenson at (202) 551 -3192, Dan Greenspan at (202)  551-3623,
or me at (202) 551 -3715 with any questions.

Sincerely,

         /s/ Daniel Greenspan for

Jeffrey P. R iedler
Assista nt Direct or

cc: Via E -mail
David S. Rosenthal, Esq.
Dechert LLP