The FDA imposed a partial hold on the global Phase 3 program for an antibody‑drug conjugate developed by Daiichi Sankyo and Merck following an unexpectedly high incidence of deaths that prompted a voluntary enrollment pause. Companies disclosed the agency’s action while investigations continue to determine causality and whether specific cohorts or dosing contributed. The hold affects global timelines for the ADC program and will likely prompt close regulatory scrutiny of safety monitoring, adjudication of causes and potential protocol amendments before resuming enrollment.