- Patients must have histologically confirmed HER2-positive invasive breast, gastric, or gastroesophageal carcinoma that is locally advanced and unresectable or metastatic and for which standard curative or palliative measures do not exist or are no longer effective; HER2-positive is defined as HER2 overexpression and/or amplification as determined by immunohistochemistry (3+) or fluorescence in situ hybridization (FISH) (>= 2.0)