Filed Pursuant to Rule 424(b)(3)
Registration Statement No. 333-253175
PROSPECTUS SUPPLEMENT NO. 4
(To prospectus dated
May 12, 2021)
Up to 29,368,920 Shares of Common Stock
This prospectus supplement no. 4 amends and supplements the prospectus dated May 12, 2021, relating to the offering and resale by the selling
stockholders identified in the prospectus of up to 29,368,920 shares of our common stock, par value $0.0001 per share (as supplemented or amended from time to time, the Prospectus).
This prospectus supplement incorporates into the Prospectus the information contained in our attached current report on
Form 8-K, which was filed with the Securities and Exchange Commission on August 17, 2021.
You should
read this prospectus supplement in conjunction with the Prospectus, including any supplements and amendments thereto. This prospectus supplement is qualified by reference to the Prospectus except to the extent that the information in the prospectus
supplement supersedes the information contained in the Prospectus.
This prospectus supplement is not complete without, and may not be delivered or
utilized except in connection with, the Prospectus, including any supplements and amendments thereto.
Our common stock is listed on the NASDAQ Global
Market under the symbol GMTX. On August 16, 2021, the last reported sale price of our common stock on the NASDAQ Global Market was $3.55.
Investment in our common
stock involves risks. See Risk Factors beginning on page 10 of the Prospectus.
Neither the Securities and Exchange Commission nor any
state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus supplement. Any representation to the contrary is a criminal offense.
The date of this prospectus supplement is August 17, 2021.