The FDA issued a partial clinical hold after a higher-than-anticipated number of deaths surfaced in a global Phase III program testing an antibody-drug conjugate (ADC) for small‑cell lung cancer. Daiichi Sankyo and Merck & Co. paused enrollment while regulators and an independent data monitoring committee review safety data. The affected program tests ifinatamab deruxtecan (I-Dxd) in relapsed small‑cell lung cancer. Trial suspensions were reported across multiple European sites and the FDA’s partial hold will require aggregated safety review before recruitment resumes. Companies said the pause applies to enrollment and recruitment while ongoing patient treatment and follow‑up continue under close monitoring. The signal raises immediate industry questions about ADC toxicities—particularly interstitial lung disease (ILD)—and will influence safety monitoring, informed‑consent language and risk mitigation in ongoing ADC programs. Regulators and sponsors are expected to re-evaluate dosing, patient selection and monitoring protocols as data are examined.