X0206 3 2021-08-10 0 0001819133 Tango Therapeutics, Inc. TNGX 0001688327 Third Rock Ventures IV, L.P. C/O THIRD ROCK VENTURES, LLC, 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001688326 Third Rock Ventures GP IV, L.P. 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 0001688325 TRV GP IV, LLC 29 NEWBURY STREET, 3RD FLOOR BOSTON MA 02116 0 0 1 0 Common Stock 19363975 D On August 10, 2021, Tango Therapeutics, Inc. (f/k/a BCTG Acquisition Corp., the "Issuer") consummated a business combination (the "Business Combination") pursuant to which BCTG Merger Sub Corp., a wholly-owned subsidiary of the Issuer merged with and into Tango Therapeutics, Inc. ("Tango"). At the effective time of the Business Combination, each share of Tango outstanding as of immediately prior to the effective time was exchanged for shares of Common Stock of the Issuer based on an exchange ratio of approximately 0.34. As a result, the Reporting Persons received 19,363,975 shares of the Issuer's Common Stock in consideration for the equity securities of Tango held by the Reporting Persons prior to the Business Combination. These shares are directly held by TRV IV. The general partner of TRV IV is Third Rock Ventures GP IV, L.P. ("TRV GP IV"). The general partner of TRV GP IV is TRV GP IV, LLC ("TRV GP IV LLC"). Each of TRV GP IV and TRV GP IV LLC disclaims beneficial ownership of these shares except to the extent of its pecuniary interest therein, if any, and this report shall not be deemed an admission that it is the beneficial owner of such shares. /s/ Kevin Gillis, Chief Operating Officer of TRV GP IV, LLC, general partner of Third Rock Ventures GP IV, L.P., general partner of Third Rock Ventures IV, L.P. 2021-08-12 /s/ Kevin Gillis, Chief Operating Officer of TRV GP IV, LLC, general partner of Third Rock Ventures GP IV, L.P. 2021-08-12 /s/ Kevin Gillis, Chief Operating Officer of TRV GP IV, LLC 2021-08-12