Sac-TMT Plus KL-A167 in PD-L1+, HR+/HER2- Metastatic Breast Cancer After CDK4/6 Inhibitors

This study is a prospective, single-arm, multicenter Phase II study designed to evaluate the efficacy and safety of Sac-TMT in combination with KL-A167 for the treatment of PD-L1-positive, HR+/HER2- metastatic breast cancer patients who previously treated with CDK4/6. The study plans to enroll 35 patients. The primary endpoint is the 6-month progression-free survival (PFS) rate assessed by the investigator (RECIST v1.1). Secondary endpoints include PFS, objective response rate (ORR), disease control rate (DCR), duration of response (DoR), overall survival (OS), and safety. An exploratory endpoint is to analyze the correlation between TROP2 and PD-L1 expression and efficacy. The treatment regimen consists of intravenous administration of Sac-TMT (5 mg/kg, Q2W) combined with KL-A167 (900 mg, Q2W). Treatment will continue until disease progression or occurrence of intolerable toxicity. Tumor assessments will be conducted every 6 weeks for the first 6 months, followed by every 12 weeks thereafter. Safety follow-up will occur after treatment completion, with telephone follow-ups every 3 months to collect survival and subsequent treatment information.