Day One Biopharmaceuticals Inc

Day One Biopharmaceuticals, Inc. is a commercial-stage biopharmaceutical company that identifies, develops, and commercializes medicines for childhood and adult diseases with equal intensity in the United States. Its lead product candidate is tovorafenib, an oral, brain-penetrant type II rapidly accelerated fibrosarcoma kinase inhibitor in Phase II clinical trials for pediatric patients with relapsed or refractory low-grade glioma; Ipsen is a frontline raf-altered pLGG in Phase III clinical trials. The company is also developing DAY301, a PTK7-targeted ADC composed of a novel humanized anti-PTK7 immunoglobulin G1 monoclonal antibody conjugated with a topoisomerase I inhibitor via a highly stable and hydrophilic modified valine-alanine (VA) cleavable linker for the treatment of patients with advanced solid tumors, and Emi-Le, an antibody-drug conjugate targeting B7-H4 conjugated to an auristatin anti-tubulin payload as a component of a proprietary linker-payload platform developed by Mersana Therapeutics, in Phase 1 clinical trials for the treatment of breast cancer, ovarian cancer, endometrial cancer, and adenoid cystic carcinoma (ACC). Day One Biopharmaceuticals, Inc. was incorporated in 2018 and is headquartered in Brisbane, California. As of April 22, 2026, it operates as a subsidiary of Servier Pharmaceuticals LLC.