Theseus Pharmaceuticals, Inc., a biopharmaceutical company, engages in the discovery, development, and commercialization of targeted therapies for the treatment of cancer patients. Its lead product candidate is THE-630, a pan-variant inhibitor for activating and resistance mutations of the KIT kinase or a pan-KIT inhibitor for the treatment of gastrointestinal stromal tumors (GIST), a type of cancer characterized by oncogenic activation of KIT. The company also develops fourth-generation EGFR inhibitor that is active against C797S, an EGFR mutation that causes resistance to first- or later-line osimertinib treatment in patients with non-small cell lung cancer. Its development programs address drug resistance mutations in key driver oncogenes, which are mutated genes that cause cancer. The company was incorporated in 2017 and is based in Cambridge, Massachusetts.