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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ( 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 ΤΟ CULLINAN ONCOLOGY , INC . ( Exact name of Registrant as specified in its Charter ) Delaware ( State or other jurisdiction of incorporation or organization ) One Main Street Suite 520 Cambridge , MA ( Address of principal executive offices ) Commission File Number : 001-39856 Securities registered pursuant to Section 12 ( b ) of the Act : 81-387991 ( I.R.S. Employer Identification No. ) Registrant's telephone number , including area code : ( 617 ) 410-4650 Trading Symbol ( s ) CGEM 02142 ( Zip Code ) Name of each exchange on which registered The Nasdaq Global Select Market Title of each class Common Stock , par value $ 0.0001 per share Securities registered pursuant to Section 12 ( g ) of the Act : None 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 15 ( d ) of the Act . YES NO > 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 . YESNO 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 , 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 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 . 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 . □ Indicate by check mark whether the Registrant is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . YES NO The registrant's common stock began trading on The Nasdaq Global Select Market on January 8 , 2021. As of January 12 , 2021 , the aggregate market value of the registrant's voting and non - voting common stock held by non - affiliates ( without admitting that any person whose shares are not included in such calculation is an affiliate ) computed by reference to the price at which the common stock was last sold on January 12 , 2021 was $ 824,134,910 . The registrant has provided this information as of January 12 , 2021 because the registrant was not a public company as of the last business day of its most recently completed second fiscal quarter and therefore cannot calculate the aggregate market value of its voting and non - voting equity held by non - affiliates as of such date . The number of shares of the registrant's common stock outstanding as of February 28 , 2021 was 43,516,125 . DOCUMENTS INCORPORATED BY REFERENCE Part III of this Annual Report on Form 10 - K incorporates by reference certain information from the registrant's definitive Proxy Statement for its 2021 annual meeting of shareholders , which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant's fiscal year end of December 31 , 2020. Except with respect to information specifically incorporated by reference in this Form 10 - K , the Proxy Statement is not deemed to be filed as part of this Form 10 - K .