The China National Medical Products Administration (NMPA) issued a new indication approval for Sichuan Kelun-Biotech Biopharmaceutical Co., Ltd’s TROP-2-targeted antibody drug conjugate (ADC) sacituzumab tirumotecan (sac-TMT; SKB264/MK-2870). The ADC can now be used in China to treat adults with unresectable locally advanced or metastatic hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer, in patients previously treated with endocrine therapy and at least two systemic therapies in the advanced setting. Approval was granted following the NMPA’s award of priority review status.

The approval is backed by data from a Phase III randomized, open-label, multi-center clinical trial (OptiTROP-Breast01) which evaluated sac-TMT monotherapy compared to chemotherapy. The trial met the primary endpoint by achieving statistically significant progression-free survival (PFS) improvement.

Sac-TMT is a TROP-2 directed ADC featuring a site-specifically conjugated topoisomerase I inhibitor payload. TROP-2 is a cell-surface antigen overexpressed in various epithelial tumors, including over 80% of breast cancers. The molecule was discovered by Kelun-Biotech and is the subject of a 2022 strategic collaboration with Merck & Co., Inc., under which Merck holds exclusive rights to develop and commercialize sac-TMT outside of Greater China.

This fourth indication approval in China follows previous NMPA nods for EGFR-positive non-squamous non-small cell lung cancer (NSCLC) patients, one indication covering patients previously treated with EGFR-TKI therapy and chemotherapy, and another for patients previously treated with EGFR-TKI alone; and for unresectable locally advanced or metastatic triple-negative breast cancer (TNBC) after at least two prior systemic therapies.

Kelun-Biotech has initiated nine registrational clinical studies in China, while Merck has at least 16 ongoing Phase III studies for sac-TMT as a monotherapy or as part of combination regimens, including with Keytruda (pembrolizumab), covering a range of cancers such as breast, lung, endometrial, ovarian, bladder, and gastroesophageal cancers. Merck picked up an FDA priority review voucher for sac-TMT in December 2025, potentially enabling a future regulatory review to be shortened to one to two months.

Notably, in November 2025 Kelun released Phase III data generated in China demonstrating sac-TMT plus Keytruda achieved PFS endpoint as well as showing positive overall survival trends in the first-line setting for PD-L1-positive NSCLC.

Industry context

The competitive landscape for ADCs in HR+/HER2- breast cancer is rapidly evolving. Currently, the standard of care in the US for pre-treated metastatic HR+/HER2- breast cancer includes Gilead Sciences’ TROP-2 ADC Trodelvy (sacituzumab govitecan), and Daiichi Sankyo/AstraZeneca’s HER2-directed ADC Enhertu (fam-trastuzumab deruxtecan-nxki). Daiichi/AstraZeneca also secured two US FDA approvals in 2025 for the TROP-2 ADC Datroway (datopotamab deruxtecan), for HR+/HER2 – breast cancer, and for previously treated EGFR+ NSCLC.

Other ADCs in late-stage clinical development for HR+/HER2- breast cancer include Daiichi Sankyo’s HER3-targeted patritumab deruxtecan, Byondis’ HER2-targeted trastuzumab duocarmazine (SYD985), and Ambrx/Sino Biopharm’s HER2-targeted ARX788.