RecruitingPhase 2Drug trialSac-TMT Plus KL-A167 in PD-L1+, HR+/HER2- Metastatic Breast Cancer After CDK4/6 InhibitorsThis is a Phase II single-arm study designed to evaluate the efficacy and safety of Sac-TMT + KL-A167 in 35 patients with PD-L1+, HR+/HER2- metastatic breast cancer who previously treated with CDK4/6 inhibitor. The primary endpoint is the 6-month PFS rate. Treatment will continue until disease progression or intolerable toxicity, with periodic imaging assessments and survival follow-up.