Response Prediction of Hyperthermic Intraperitoneal Chemotherapy in Gastro- Intestinal Cancer

Inclusion Criteria: * (Suspected) synchronous or metachronous peritoneal metastasis of adenocarcinoma of the stomach / gastroesophageal junction (GEJ) or of the colon or rectum * intraoperative histological confirmation of synchronous or metachronous peritoneal carcinomatosis in gastric carcinoma (incl. GEJ) or colon carcinoma (incl. rectal carcinoma) * Intraoperative peritoneal cancer index (PCI) ≤ 15 for gastric carcinoma and ≤ 20 for colon carcinoma. * Possibility of surgical resection of peritoneal carcinomatosis (cytoreductive surgery) in curative intention with achievement of a Completeness of Cytoreduction Score (CCS) of 0-1 * No contraindication to surgery * No contraindication against the performance of HIPEC * Expected survival of 6 months at least * ECOG ≤ 2 * Female and male patients ≥ 18 years of age * Patient is able and willing to give written informed consent and comply with the study protocol Exclusion Criteria: * Presence of non-resectable distant metastases * Patients with extensive metastasis (e.g., multiple bilobular liver metastases, hepatic and pulmonary metastases, multiple retroperitoneal lymph node metastases; oligometastasis is allowed) * Patients with recurrence of peritoneal carcinomatosis (e.g., previous peritonectomy in the course of primary tumor resection) * Patients after previous palliative chemotherapy or radiation of the tumor (exception: neoadjuvant and/or adjuvant therapies) * Hypersensitivity/allergy to components of the planned intraperitoneal chemotherapy * Patients not eligible for surgery/HIPEC (e.g., heart failure NYHA ≥III, myocardial infarction within the last 3 months before surgery, high-risk cardiac arrhythmias) * Secondary malignant disease that occurred \<5 years ago (exception: early stage of a localized tumor with in-sano resection, for example in situ carcinoma of the cervix, Adequately treated basal cell carcinoma of the skin) * Patients who are housed in a closed facility * Pregnant or breastfeeding patients, or patients who plan to become pregnant within 7 Months after the end of treatment to become pregnant