The U.S. FDA accepted and granted priority review to Daiichi Sankyo and Merck & Co.’s B7-H3-directed antibody-drug conjugate, ifinatamab deruxtecan, for advanced extensive-stage small-cell lung cancer. The agency’s priority review of the BLA increases urgency around an expected regulatory decision date and underscores the drug’s perceived differentiation. Priority review designations typically compress timelines for FDA action and reflect that the agency believes the application merits expedited assessment under statutory review processes. The therapy targets B7-H3, a tumor-associated antigen relevant to small-cell lung cancer biology and resistance. For oncology developers, the designation is a concrete regulatory milestone that can materially shift market expectations for the B7-H3 ADC category and for antibody-drug conjugates targeting solid tumor antigens beyond traditional HER2-like pathways.