Phase II Clinical Trial of PD-L1 in Combination With Vinorelbine + Cyclophosphamide + Capecitabine (VEX) Metronomic Chemotherapy With or Without Radiotherapy for Advanced Triple-negative Breast Cancer.

Male or female who is 18 years of age or older on the day of signing the informed consent form.

Subjects with metastatic triple-negative breast cancer, with clear clinical data records; specific reference to the "American Society of Clinical Oncology - College of American Pathologists (ASCO/CAP) guidelines."

Have received less than or equal to 1 line of chemotherapy for metastatic breast cancer;

Have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 as assessed within 10 days before the start of study treatment;