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Table of Contents ( Mark One ) ☑ ☐ UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 FORM 10 - Q QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended June 30 , 2021 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number : 001-38984 CASTLE BIOSCIENCES , INC . ( Exact name of registrant as specified in its charter ) Delaware ( State or other jurisdiction of incorporation or organization ) 505 S. Friendswood Drive , Suite 401 , Friendswood , Texas ( Address of principal executive offices ) ( 866 ) 788-9007 ( Registrant's telephone number , including area code ) 77-0701774 ( I.R.S. Employer Identification No. ) 77546 ( Zip Code ) Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Common Stock , $ 0.001 par value per share Trading Symbol ( s ) CSTL Name of each exchange on which registered The Nasdaq Global Market 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 ☐ ☑ ☑ Accelerated filer Smaller reporting company Emerging growth company 冈 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 is a shell company ( as defined in Rule 12b - 2 of the Exchange Act ) . Yes No As of July 30 , 2021 , there were 25,167,365 shares of common stock , $ 0.001 par value per share , issued and outstanding .