Monotherapy for the treatment of adult patients w/ unresectable or metastatic HER2 +ve breast cancer who have received ≥1 prior anti-HER2-based regimens. Monotherapy for the treatment of adult patients w/ unresectable or metastatic HER2-low breast cancer who have received prior chemotherapy in the metastatic setting or developed disease recurrence during or w/in 6 mth of completing adjuvant chemotherapy. Monotherapy for the treatment of adult patients w/ advanced HER2 +ve gastric or gastroesophageal junction adenocarcinoma who have received a prior trastuzumab-based regimen.