The purpose of this research is to collect surgical drain fluid and blood from patients who have undergone surgery for gastric or esophageal cancer, and to analyze the fluid and blood using a variety of laboratory techniques for molecular markers capable of predicting response to immunotherapy.

Inclusion Criteria:

• Patients undergoing esophagectomy or gastrectomy for gastroesophageal cancer.
• Adult males and females at least 18 years of age
• Ability to complete testing in the protocol and attend study visits
• Able and willing to consent to protocol
• Adequate organ function Absolute Neutrophil Count (ANC) ≥1.5 x 103/μL Platelets ≥100 x 103/μL Hemoglobin >9.0 g/dL Total Bilirubin (</= 2.0 mg/dl at time of Y90 radioembolization) AST/ALT ≤5 x upper limit of normal Albumin >3 g/dL Creatinine ≤1.5 mg/dL

Exclusion Criteria:

• Female patients who are pregnant or breast-feeding
• Concomitant illness that would prevent adequate patient assessment or in the investigators' opinion pose an added risk for study participants.
• Life-threatening intercurrent illness
• Anticipated poor compliance
• Prisoners or subjects who are involuntarily incarcerated
• Persons with decisional incapacity/cognitive impairment
• Any history or evidence of severe illness or any other condition that would make the patient, in the opinion of the investigator unsuitable for the study
• Subject is enrolled in a separate interventional clinical trial

Adult males and females at least 18 years of age undergoing esophagectomy or gastrectomy for gastroesophageal cancer