UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, DC 20549 x QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2020 Or ¨ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number: 001-36020 Onconova Therapeutics, Inc. (Exact name of registrant as specified in its charter) Delaware 22-3627252 (State or other jurisdiction of (I.R.S. Employer incorporation or organizat ...