Peritoneal carcinomatosis (PC) in gastric cancer (GC) is considered a fatal disease, without expectation of definitive cure. Since conventional surgery is not indicated in the palliative setting, and systemic chemotherapy treatments are not sufficient to contain the disease, a multimodal approach associating intraperitoneal (IP) chemotherapy (CMT) with surgery may represent an alternative for these patients.

IP CMT has shown superior results to conventional treatment in patients at this stage of the disease, and can achieve complete regression of lesions in a significant portion of cases. Once response to treatment is achieved, patients become fit for curative surgery, which offers a new perspective on the survival in these previously unresectable cases, and raising survival rates to similar levels to patients undergoing surgery with curative intention.

Thus, the aim of this study is to evaluate the complete response rate and curative resection in patients with PC by GC at Instituto do Cancer do Estado de São Paulo (ICESP) treated with IP CMT. Patients prospectively included in the study will undergo implantation of a peritoneum catheter to perform outpatient IP CMT in order to promote the regression of lesions. Those with complete regression may be referred for surgical treatment, curing a portion of these patients. The diagnosis of PC will be performed by conventional cytological, immunohistochemical and liquid cytology methods to determine the presence of tumor cells in the peritoneal lavage and to evaluate the sensitivity of the methods. In addition, it is proposed in the study the storage of material for further study of circulating markers in peripheral blood and peritoneal lavage that may be related to response or resistance to treatment.

It is believed that IP CMT may not only increase the survival of patients with PC, but also offer the possibility of cure for a significant portion of patients who are currently without treatment prospects and with a median survival of only six months.

This is a prospective study lasting 36 months.

Inclusion Criteria:

• Gastric adenocarcinoma
• Presence of peritoneal carcinomatosis documented through intraoperative identification and confirmed by biopsies and/or positive oncotic cytology;
• Presence of exclusively peritoneal metastasis with PCI < 12;
• Age between 18 and 75 years;
• Eastern Cooperative Oncology Group (ECOG) performance scale 0 and 1;
• Body mass index (BMI) greater than 18;
• Total WBC count ≥3000, neutrophils ≥1500, hemoglobin ≥8, and platelet count ≥100,000;
• Bilirubin <2, TGO/TGP/FA/GGT 3x the reference value;
• Creatinine clearance calculated by the Cockcroft-Gault formula ≥ 50 ml/min.

Exclusion Criteria:

• Synchronous or metachronic neoplasms;
• Previous antineoplastic treatment for gastric cancer;
• Clinical conditions considered critical by the investigator;
• Obstruction of the digestive tract;
• Suspected gastrointestinal bleeding;
• New York Heart Association functional class II/III/IV heart failure;
• Heart disease that, in the opinion of the investigator, prevents the patient from receiving the necessary hydration during chemotherapy with cisplatin.
• Known HIV infection or chronic use of immunosuppressants;
• Acute myocardial infarction or stroke in the last 6 months
• pregnant.