Part A is a Dose-Escalation Study in Participants with Relapsed or Refractory Esophageal Cancer or Gastro-Esophageal Junction Tumors. Parts B, C, D and E are expansion cohorts of Patients with Relapsed or Refractory Esophageal Cancer, Gastro-Esophageal Junction Tumors and Gastric Adenocarcinoma.