Study of SKB264 for Locally Advanced, Recurrent or Metastatic HR+/HER2- Breast Cancer

This study tests a new antibody-drug treatment called SKB264 in patients with hormone receptor-positive, HER2-negative breast cancer (HR+/HER2-) that has spread or returned and stopped responding to prior chemotherapy. SKB264 delivers a chemotherapy drug directly to cancer cells using a targeted antibody. **You may be eligible if...** - You are 18 to 75 years old - You have HR+/HER2- breast cancer confirmed by biopsy that has spread or returned - You have already tried and failed at least one prior chemotherapy regimen - You have at least one measurable tumor - Your overall health is good (ECOG 0-1) - Your organ function and blood counts are adequate **You may NOT be eligible if...** - Your cancer has spread to the brain - You have had another cancer within the last 3 years (except certain skin cancers) - You have active hepatitis B, hepatitis C, or HIV infection - You have had prior treatment with a TROP2-targeted drug or topoisomerase I inhibitor - You are pregnant or breastfeeding - You have a serious lung condition or history of lung inflammation (ILD) Talk to your doctor to see if this trial is right for you.