Kumorixilib Plus Capecitabine and Letrozole for Neoadjuvant Treatment of HR-Positive HER2-Negative Breast Cancer

This study is a single-center, prospective, open-label exploratory clinical study to assess the efficacy and safety of kumorixilib combined with capecitabine and letrozole as neoadjuvant therapy in patients with HR+/HER2- stage II-III invasive breast cancer. The study plans to enroll 35 eligible patients, and all participants will receive the triple-drug combination regimen without randomization. The treatment regimen: kumorixilib 180 mg orally once daily, capecitabine 500 mg orally three times daily, and letrozole 2.5 mg orally once daily; each cycle lasts 28 days, for a total of 6 cycles. Breast MRI will be used to evaluate radiological tumor response. Surgical resection will be arranged 2-4 weeks after neoadjuvant treatment ends. The primary endpoint is the percentage change in Ki-67 score from baseline to Cycle 1 Day 28. Secondary endpoints include the complete cell cycle arrest rate (CCCA, Ki-67 ≤ 2.7%) on Day 28, the reduction rate of functional tumor volume (FTV), the proportion of patients with RCB 0-1, objective response rate (ORR), and treatment safety. Treatment will be discontinued upon disease progression, intolerable adverse events, withdrawal of consent, or investigator judgment.