Theseus Pharmaceuticals, a biotechnology company shaping the future of targeted oncology by developing best-in-class, pan-variant kinase inhibitors, emerged from stealth today announcing the close of a $100 million Series B financing led by Foresite Capital. Theseus also announced data from a poster presentation at the American Association for Cancer Research (AACR) 2021 Annual Meeting, which demonstrated that the Company's lead product candidate, THE-630, has potent activity against all major classes of activating and resistance mutations observed in patients with KIT-mutant gastrointestinal stromal tumors (GIST).

OrbiMed incubated Theseus to develop therapies designed to outsmart treatment-resistant cancer mutations, funding the Company's Series A in 2018. In addition to Foresite Capital, the Series B raise was supported by a syndicate of other new investors, including Adage Capital Management, Boxer Capital, Farallon Capital Management, Longitude Capital, Nextech Ventures, Omega Funds, Pontifax Venture Capital, Rock Springs Capital, and T. Rowe Price, as well as OrbiMed. In conjunction with the financing, Michael Rome, Ph.D., Managing Director of Foresite Capital, has joined the Theseus Board of Directors, which also includes Carl Gordon, General Partner at OrbiMed.

Theseus Pharmaceuticals is passionately committed to outsmarting cancer resistance. The Company is developing best-in-class, pan-variant kinase inhibitors, to shape the future of targeted oncology. Theseus believes truly transformative, targeted oncology therapeutics must inhibit all clinically relevant variants. Led by a team of pioneers in the discovery and development of tyrosine kinase inhibitors (TKIs), the Company's technology can predict how a cancer will mutate, enabling Theseus to target known mutations, stay ahead of future variants, and overcome the demonstrated burden of treatment resistance. For more information, visit www.theseusrx.com.