Newly Diagnosed Triple-negative Breast Cancer

This study is a multicenter, randomized controlled phase III clinical trial. The aim of this study is to observe the efficacy and safety of PD-1 inhibitors combined with capecitabine, PD-1 inhibitors alone, or capecitabine alone in patients with TNBC who have residual lesions after neoadjuvant treatment. The subjects will be randomly assigned in a 1:1:1 ratio to Group A (capecitabine combined with PD-1 inhibitor), Group B (PD-1 inhibitor), and Group C (capecitabine). The stratification factors are the lymph node metastasis status (lymph node metastasis negative ypN0, lymph node metastasis positive ypN1-3) and PD-L1 status (negative/positive) after neoadjuvant treatment. Group A: Capecitabine, 1250mg/m2, twice a day, 14/21 days, combined with PD-1 inhibitor, for a total of 8 cycles Group B: PD-1 inhibitor, for a total of 8 cycles Group C: Capecitabine, 1250mg/m2, twice a day, 14/21 days, for a total of 8 cycles The study will include approximately 10 centers. After the completion of NAT (chemotherapy + immunotherapy), 852 patients with residual lesions (breast still has invasive cancer lesions remaining and/or positive axillary lymph nodes) will be enrolled, with 284 patients in each of Groups A, B, and C. After surgery, clinicians will, based on clinical treatment guidelines and the clinical practices of each center, administer radiotherapy to subjects with indications for radiotherapy. During radiotherapy, the use of capecitabine and/or immunotherapy is decided by the supervising doctor as either concurrent or sequential.