PERitoneal Carcinomatosis LEveraging ctDNA guided treatment Study in GI Cancer (PERICLES Study).

Inclusion Criteria: - Patients with histologically confirmed carcinoma of presumed gastrointestinal origin (gastric, esophageal, colorectal, appendiceal, hepatobiliary or peritoneal carcinomatosis of apparent GI primary) with documented diffuse peritoneal carcinomatosis, either by conventional imaging studies, positive ascitic fluid analysis, or surgical staging - Measurable or evaluable disease by cross-sectional imaging studies - Patients must be candidates for possible surgical cytoreduction (with or without HIPEC) as determined by a study surgical oncologist - Age >= 18 years - Estimated life expectancy of at least 12 months - Eastern Cooperative Oncology Group (ECOG) performance status =< 2 - Patients must sign informed consent - Be willing to present for medical exams, blood draws and imaging as scheduled in protocol - Be able to donate two 10 mL tubes of blood every 3 months - Women of childbearing potential will undergo routine screening evaluation for pregnancy prior to enrollment and be managed per standard of care Exclusion Criteria: - Patients without a confirmed pathologic diagnosis of carcinoma - Second uncontrolled primary malignancy - Patients who are pregnant - Patients who cannot undergo a therapeutic surgical cytoreduction - Bone marrow transplant or other organ transplant recipient - Any unstable, serious co-existing medical conditions including but not limited to myocardial infarction, coronary bypass surgery, unstable angina, cardiac arrhythmias, clinically evident congestive heart failure, or cerebrovascular accident within 6 months prior to screening - Patients with cardiovascular or pulmonary risk factors contributing to high risk for surgical complications, at the discretion of the surgeon - Serious concomitant systemic disorder that would compromise the safety of the patient or compromise the patient's ability to complete the study, at the discretion of the investigator