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 Cance

• Metastatic or unresectable BC histologically confirmed to be either HER2 positive (IHC 3+ or ISH positive) or HER2 low (IHC 1+ or 2+ and negative ISH). Must be documented before having received T-DXd treatment previously
• Must have previously received T-DXd
• Measurable disease
•  At leat 1 but no more than 3 prior chemo-based regimens in the metastatic /unresectable setting. If gotten in adjuvant setting but recurred within 6 months, this would count as a line of therapy
• ECOG PS 0-1
• If HR-positive HER2-low, must have received endocrine therapy in the past and not be expected to have further benefit
• No active CNS mets
• No prior eribulin treatment
• No active pneumonitis or ILD
• No CHF greater than NYHA Class II or LVEF <50%
• No known history of TB
• HIV allowed if CD4+ <350 and viral load <400
• HBV allowed if willing and able to take anti HBV therapy
• HCV only allowed if completed curative therapy

• Primary
  • Part 1
    • Safety
  • Part 2
    • ORR
• Secondary
  • DOR
  • DCR
  • TTR
  • CBR
  • PFS
  • OS
  • Safety