U.S. regulators and sponsors paused a global Phase 3 antibody‑drug conjugate (ADC) program after an unexpectedly high number of on‑study deaths. Daiichi Sankyo and Merck stopped enrollment and the FDA placed a partial hold on the trial, citing safety signals under review. The move affects a late‑stage oncology asset that had been a key development program for both companies and will delay pivotal readouts and potential filing timelines. ADCs combine targeted antibodies with cytotoxic payloads; unexpected mortality in late‑stage ADC trials triggers intensified safety review given the modality’s potency.