Subjects must meet all eligibility criteria. The key inclusion and exclusion criteria are as follows:  Key Inclusion Criteria:  All subjects must have metastatic esophageal or gastroesophageal junction carcinomas (adenocarcinoma only) ECOG performance status of 0 or 1 Tumor tissue must be available for correlative studies - Either a formalin fixed paraffin block or a minimum of ten 5-micron tissue section's (slides) of tumor biopsy sample must be available for biomarker evaluation. Patients must have received at least one prior line of standard systemic therapy for recurrent or Stage IV disease, and that patients with HER2 overexpression have received an anti-HER2 drug.  Key Exclusion Criteria:  Squamous cell carcinomas Mixed histology with small cell component