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( Mark One ) X UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 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 ΤΟ Commission File Number 001-38459 Delaware ( State or other jurisdiction of incorporation or organization ) Title of each class Common stock , $ 0.0001 FORM 10 - K 50 Hampshire Street , 8th Floor Cambridge , MA ( Address of principal executive offices ) Large accelerated filer Non - accelerated filer SURFACE ONCOLOGY , INC . ( Exact name of Registrant as specified in its Charter ) X Registrant's telephone number , including area code : ( 617 ) 714-4096 Securities registered pursuant to Section 12 ( b ) of the Act : Trading Symbol ( s ) SURF Securities registered pursuant to Section 12 ( g ) of the Act : None ( Title of class ) 46-5543980 ( I.R.S. Employer Identification No. ) Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes ¨ No X Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15 ( d ) of the 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 such filing requirements for the past 90 days . Yes x 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 x No " 02139 ( Zip Code ) Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , 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 . Name of exchange on which registered The Nasdaq Global Market Accelerated filer Smaller reporting company 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 . x DOCUMENTS INCORPORATED BY REFERENCE X X Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No X The aggregate market value of the registrant's common stock , $ 0.0001 par value per share ( " Common Stock " ) , held by non - affiliates of the registrant , based on the last sale price of the Common Stock at the close of business on June 30 , 2020 , was $ 205,919,004 . For purposes of foregoing calculation only , all directors and executive officers of the registrant are assumed to be affiliates of the registrant . The number of shares of registrant's Common Stock outstanding as of March 5 , 2021 was 41,727,725 . Portions of the registrant's Definitive Proxy Statement relating to the Annual Meeting of Shareholders , scheduled to be held on June 8 , 2021 , are incorporated by reference into Part III of this Report .