ARX788 in Selected HER2-mutated or HER2-amplified/Overexpressed Solid Tumors (ACE-Pan Tumor-02)

Inclusion Criteria: * Age ≥ 18 years and older * Life expectancy \> 3 months * Eastern Cooperative Oncology Performance Status ≤ 1 * HER2 status must be determined from a local Clinical Laboratory Improvement Amendments (CLIA) or equivalent-certified laboratory. * Cohort 1, Cohort 2, and Explanatory Cohort A: HER2 mutated subjects with pre-specified HER2 activating mutation. Subjects with HER2 mutations in NSCLC (Cohort 1), breast cancer (Cohort 2), and other solid tumors (Cohort A) who have not received prior HER2 antibody drug conjugate (ADC) treatment are eligible. * Cohort 3: Subjects with HER2 amplifications in biliary tract cancers (BTC) who have not received prior HER2 ADC treatment are eligible. * Cohort 4: Subjects with HER2 amplifications in colorectal cancer (CRC), ovarian, endometrial, NSCLC and other solid tumors who have not received prior HER2 ADC treatment are eligible. * Cohort 5 HER2 mutation or HER2 amplification: subjects with HER2 mutated or amplified tumors and have been previously treated with HER2 ADC are eligible. * Subjects who are resistant or refractory to previous standard care of treatment. * Subjects with stable brain metastases. * Adequate organ functions. Exclusion Criteria: Any subject who meets any of the following criteria is excluded from the study: * For Cohort 4: breast and gastric/GEJ cancer are excluded. * Prior history of interstitial lung disease, pneumonitis, or other clinically significant lung disease within 12 months. * Histo…