The FDA placed a partial hold on Daiichi Sankyo and Merck & Co.’s global Phase 3 program for their investigational antibody‑drug conjugate (ADC) after investigators paused enrollment citing a "higher than anticipated incidence" of deaths. Both companies disclosed the safety signal and the FDA ordered a targeted review that halted new patient enrollment in affected cohorts. Clinical operations and safety committees are coordinating data reviews to determine whether dosing changes, protocol amendments or wider holds are required. The development affects a large, late‑stage oncology program and will prompt regulators and sponsors to scrutinize ADC payload safety across pipelines. Daiichi Sankyo and Merck are working with investigators and the FDA; the agencies will weigh whether the deaths are treatment‑related or reflect advanced disease and comorbidity. The outcome will influence ADC risk‑benefit discussions and ongoing global registrational plans.