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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - K ( Mark One ) ☑ ㅁ 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 Delaware Commission File Number 001-39386 ALX ONCOLOGY HOLDINGS INC . ( Exact name of Registrant as specified in its Charter ) ( State or other jurisdiction of incorporation or organization ) 866 Malcolm Road , Suite 100 Burlingame , California ( Address of principal executive offices ) 85-0642577 ( I.R.S. Employer Identification No. ) 94010 ( Zip Code ) Registrant's telephone number , including area code : 650-466-7125 Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Common Stock , par value $ 0.001 per share Securities registered pursuant to Section 12 ( g ) of the Act : None Trading Symbol ( s ) ALXO Name of each exchange on which registered The Nasdaq Global Select Market 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 . 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 ☐ ☑ ☑ Accelerated filer Smaller reporting 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 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 aggregate market value of the common stock held by non - affiliates of the Registrant , based on the closing price of the shares of common stock on The Nasdaq Stock Market on December 31 , 2020 , was $ 1.5 billion . The Registrant has elected to use December 31 , 2020 as the calculation date , which was the last trading date of the Registrant's most recently completed fiscal year , because on June 30 , 2020 ( the last business day of the Registrant's most recently completed second fiscal quarter ) , the Registrant was a privately held company . Shares of common stock owned by each executive officer , director , and holder of more than 5 % of the Registrant's common stock have been excluded in that such persons may be deemed to be affiliates of the Registrant . This calculation does not reflect a determination that certain persons are affiliates of the Registrant for any other purpose . The number of shares of Registrant's Common Stock outstanding as of March 12 , 2021 was 40,127,198 . DOCUMENTS INCORPORATED BY REFERENCE Certain portions of the registrant's definitive proxy statement relating to the Company's 2021 Annual Meeting of Stockholders , to be filed with the Securities and Exchange Commission within 120 days of the registrant's fiscal year ended December 31 , 2020 , are incorporated by reference into Part III of this Annual Report on Form 10 - K where indicated .