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Table of Contents UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 ( Mark One ) ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Transition Period from FORM 10 - K Delaware ( State or Other Jurisdiction of Incorporation or Organization ) Commission File Number : 001-36812 SALARIUS PHARMACEUTICALS , INC . ( previously known as Flex Pharmaceuticals , Inc. ) ( Exact name of Registrant as Specified in Its Charter ) Title of each class Common Stock , par value $ 0.0001 to 2450 Holcombe Blvd. , Suite X , Houston , TX 77021 ( Address of principal executive offices ) ( Zip Code ) Registrant's Telephone Number , Including Area Code : ( 832 ) 834-6992 Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) 46-5087339 ( I.R.S. Employer Identification No. ) □ ☑ □ SLRX Securities registered pursuant to Section 12 ( g ) of the Act : None . Name of each exchange on which registered The Nasdaq Stock Market LLC Indicate by check mark if the registrant is a well - known seasoned issuer as defined in Rule 405 of the Securities Act . Yes No Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15 ( d ) of the Exchange Act . Yes No X Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to the filing requirements for the past 90 days . Yes No Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( § 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of large accelerated filer , accelerated filer , smaller reporting company , and emerging growth company in Rule 12b - 2 of the Exchange Act . Large Accelerated Filer Non - accelerated Filer Emerging Growth Company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . As of March 15 , 2021 , there were 44,734,328 shares of common stock outstanding . DOCUMENTS INCORPORATED BY REFERENCE : Accelerated Filer Smaller Reporting Company Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act . ) Yes No The aggregate market value of the common stock of the registrant held by non - affiliates of the registrant is $ 19,157,672 based on a share price of $ 1.32 which is the closing price per share on June 30 , 2020 . Portions of the registrant's definitive proxy statement for its 2021 Annual Meeting of Stockholders , which will be filed with the United States Securities and Exchange Commission within 120 days of December 31 , 2020 , are incorporated by reference into Part III of this Annual Report on Form 10 - K .