Day One Biopharmaceuticals, Inc., a commercial-stage biopharmaceutical company, engages in the identification, development, and commercialization of medicines for childhood and adult diseases with equal intensity in the United States. The company's lead product candidate is tovorafenib, an oral and brain-penetrant type II rapidly accelerated fibrosarcoma kinase inhibitor that is in Phase II clinical trial for pediatric patients with relapsed or refractory low-grade glioma; and Ipsen, a frontline raf-altered pLGG which is in Phase III clinical trial stage. It 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 that targets B7- H4 conjugated to an auristatin anti-tubulin payload as a component of a proprietary linker-payload platform developed by Mersana Therapeutics that is in Phase 1 clinicla trial 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, Day One Biopharmaceuticals, Inc. operates as a subsidiary of Servier Pharmaceuticals LLC.