Sacituzumab Govitecan +/- Pembrolizumab in Metastatic TNBC

This study is testing whether adding pembrolizumab (an immunotherapy drug) to sacituzumab govitecan (a targeted chemotherapy) improves outcomes in patients with metastatic triple-negative breast cancer (TNBC) — an aggressive form of breast cancer that does not respond to hormone-based treatments. Participants must have low or no PD-L1 expression (a marker on cancer cells). **You may be eligible if:** - You have triple-negative breast cancer (ER-negative, PR-negative, HER2-negative) that has spread or cannot be surgically removed - Your cancer has low or no PD-L1 expression - You have not yet received any treatment for metastatic disease (treatment-naive in the metastatic setting) - You have at least one measurable tumor (including bone-only disease) - You are willing to undergo tumor biopsies **You may NOT be eligible if:** - You have already received treatment for your metastatic disease - You have an active autoimmune disease requiring treatment - You are pregnant or breastfeeding - You have active, untreated brain metastases - You have significant heart, liver, or kidney dysfunction Talk to your doctor to see if this trial is right for you.