Merck and Daiichi Sankyo withdrew their FDA accelerated-approval submission for their B7-H3 antibody-drug conjugate in small cell lung cancer after FDA pushback on available data. The move erases a competitive advantage as multiple ADC programs pursue expedited pathways in the same disease space. The companies’ decision highlights the stringency of accelerated-approval evidence requirements for ADCs and could force a re-think of registrational strategies, including trial endpoints and post-marketing plans. Investors will watch how Merck and Daiichi recalibrate timelines across the ADC pipeline.