A First-in-human Study of Multiple Doses of BB-1701 in Subjects With Locally Advanced/Metastatic HER2 Expressing Solid Tumors

This is an open-label, FIH, phase 1 dose-escalation and cohort expansion study of BB-1701 in subjects with locally advanced /metastatic HER2 expressing solid tumors. The study consists of 2 parts: dose-escalation (Part 1) and cohort expansion (Part 2). Part 1 of this study will follow accelerated titration and traditional "3 + 3" design. Part 2 is a cohort expansion study with HER2 expressing locally advanced/metastatic solid tumors. Part 2 consists of 4 cohorts: Cohort 1: Patients with HER2 overexpressing or positive (defined as IHC 3+ or IHC 2+/FISH positive) locally advanced or metastatic breast cancer who have progressed on prior standard therapies including anti HER2 therapy Cohort 2: Patients with HER2 low expressing (defined as IHC 2+ /FISH negative, or IHC 1+) locally advanced or metastatic breast cancer who have progressed on prior standard therapies. Cohort 3: Patients with HER2 overexpressing or positive (defined as IHC 3+ or IHC 2+/FISH positive) locally advanced or metastatic gastric cancer or gastroesophageal junction cancer who have progressed on prior standard therapies. Cohort 4: Patients with HER2 overexpressing or positive (defined as IHC 3+, or IHC 2+/FISH positive) locally advanced or metastatic solid tumors (other than breast cancer and gastric or gastroesophageal junction cancer) who have progressed on prior standard therapies. Patients with HER2 mutation or amplification by NGS can also be enrolled in this cohort.