Merck and Daiichi Sankyo said they withdrew an FDA accelerated approval application for their B7-H3 ADC, I-DXd, in a specific small cell lung cancer population after FDA feedback indicated the available data would not support accelerated clearance. The decision erases a claimed competitive edge amid a crowded ADC landscape. The withdrawal highlights how evidentiary barometers for accelerated pathways can tighten quickly when trial endpoints or subgroup outcomes do not align with FDA expectations. The setback adds pressure on the partnership’s remaining development steps and timelines in lung cancer.