A Study of SI-B003 or BL-B01D1+SI-B003 in Patients With Unresectable Locally Advanced or Recurrent Metastatic HER2 Negative Breast Cancer

This study is testing one or two new treatments — SI-B003 alone or combined with BL-B01D1 — in patients with HER2-negative breast cancer (breast cancer that does not overexpress a protein called HER2) that has come back or spread and has not responded to standard treatments. **You may be eligible if...** - You are 18–75 years old - You have confirmed HER2-negative breast cancer that has spread or cannot be surgically removed - Your cancer has failed standard treatments or no standard treatment is available - You are in generally good health (ECOG status 0–1) - Your life expectancy is at least 3 months **You may NOT be eligible if...** - Your cancer is HER2-positive - You have serious heart, liver, or lung conditions - You have active brain metastases - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.