This study investigates if a drug called sacituzumab govitecan (SG) works well in patients with a specific type of breast cancer who have previously been treated with another drug, trastuzumab deruxtecan (T-DXd). SG is already approved for some breast cancers, but the study wants to see its effect on patients who received T-DXd first. Metastatic means the cancer has spread beyond the breast.

• The study requires participants to have tried at least 1 but not more than 4 chemotherapy treatments before.
• Participants need to be at least 18 years old, and the study involves multiple visits.
• Participants must not be pregnant or breastfeeding and should use effective birth control if of childbearing potential.

Before joining, participants will need to prove they meet certain health criteria, like having good bone marrow function and not having certain infections. This study might help find better treatments for specific breast cancer patients. Always consult with your doctor to understand the potential risks and benefits before participating.