Bortezomib Followed by Pembrolizumab and Cisplatin in metTNBC

This study is testing a combination of three drugs — bortezomib, pembrolizumab (immunotherapy), and cisplatin (chemotherapy) — for women with metastatic triple-negative breast cancer (TNBC), which is a type of breast cancer that lacks hormone receptors and is harder to treat. **You may be eligible if:** - You are a woman aged 18 or older with metastatic triple-negative breast cancer - You have previously received standard chemotherapy (anthracycline, cyclophosphamide, and taxane-based treatment) - You have not received more than 3 prior chemotherapy regimens for metastatic disease - You have measurable disease on scans and adequate organ function **You may NOT be eligible if:** - You have received more than 3 prior chemotherapy regimens for metastatic disease - You have significant heart, kidney, or other organ problems - You are pregnant or not using effective contraception - You have active autoimmune disease that required systemic treatment Talk to your doctor to see if this trial is right for you.