Adenocarcinoma of the Gastroesophageal Junction, Adenocarcinoma of the Stomach, Recurrent Gastric Cancer, Stage III Esophageal Cancer, Stage III Gastric Cancer, Stage IIIA Esophageal Cancer, Stage IIIB Esophageal Cancer, Stage IIIC Esophageal Cancer, Stage IV Esophageal Cancer, Stage IV Gastric Cancer