BB-1701-G000-205 An Open-label, Multicenter, Phase 2 Dose Optimization and Expansion Study to Evaluate the Safety and Efficacy of BB-1701, an anti-human epidermal growth factor receptor 2 (anti-HER2) antibody-drug conjugate (ADC), in Previously Treated Subjects with HER2-positive or HER2-low Unresectable or Metastatic Breast Cancer

The purpose of this study is to determine if a new drug called BB-1701 is safe and effective in people who have HER2-positive or HER2-low, unresectable or metastatic breast cancer (MBC). There are two parts of this study. The first part of this study, the Dose Optimization part (Part 1), is to determine the safest and most effective dose of BB-1701 for the treatment of breast cancer. This dose will be used in the Dose Expansion part (Part 2), to further evaluate the safety and efficacy of BB-1701 in a larger group of patients with HER2-positive or HER2-low MBC.