Merck & Kelun-Biotech's sac-TMT meets Phase 3 TNBC primary endpoint. Merck & Kelun-Biotech's sac-TMT hit primary endpoint. Phase 3 OptiTROP-Breast03 study succeeded. Progression-free survival (PFS) improved. First-line TNBC treatment potential emerges. Merck & Co. and Kelun-Biotech announced their antibody-drug conjugate (ADC), sacituzumab tirumotecan (sac-TMT), met its primary endpoint in the Phase 3 OptiTROP-Breast03 study. The trial evaluated sac-TMT as a first-line treatment for advanced triple-negative breast cancer (TNBC). The key metric, progression-free survival (PFS), improved compared to chemotherapy, signaling a major clinical advance for this difficult-to-treat cancer. This positive outcome paves the way for regulatory submissions. Under FDA guidelines, successful Phase 3 data supports a New Drug Application (NDA). EMA procedures will similarly require a Marketing Authorization Application (MAA). The companies will now compile comprehensive data for review, adhering to 21 CFR Part 314 for NDA submissions. Expedited review pathways may be pursued given the unmet medical need in TNBC. The positive data strengthens Merck and Kelun-Biotech's position in the competitive TROP2 ADC market. This success validates their partnership and challenges existing players like Gilead's Trodelvy (sacituzumab govitecan). The results could shift treatment paradigms for first-line TNBC. Expect regulatory filings to commence by Q4 2026, intensifying competition in this therapeutic area.