Background: The main reason for treatment failure after curative surgical resection of gastric cancer is intra-abdominal spread, with 40- 50% peritoneal seeding as primary localization of recurrence. Peritoneal relapse is seen in 60-70% of tumors of diffuse type, compared to only 20-30% of intestinal type. Hyperthermic IntraPEritoneal Chemoperfusion (HIPEC) is an increasingly used therapy method for patients with peritoneal metastases. The preventive use of HIPEC could represent an elegant approach for patients (pts) before macroscopic peritoneal seeding, since patients with operable disease are fit and may have potential risk of microscopic involvement, thus having a theoretical chance of cure with HIPEC even without the need for cytoreduction. No results from a PCRT from the Western hemisphere have yet been published. Methods: This is a multicenter, randomized, controlled, open-label study including a total of 200 pts with localized and locally advanced diffuse and mixed type (Laurens`s classification) adenocarcinoma of the stomach and Type II/III GEJ (i.e. ≥cT3 any N or any T N positive). All enrolled pts will have received 3-6 pre-operative cycles of biweekly FLOT (Docetaxel 50 mg/m²; Oxaliplatin 85 mg/m²; Leucovorin 200 mg/m²; 5-FU 2600 mg/m², q2wk). Pts will be randomized 1:1 to receive surgery only and postoperative FLOT (Arm A- Control arm) or surgery + intraoperative HIPEC (cisplatin 75mg/m2 solution administered at a temperature of 42°C for 90 minutes) and postoperative FLOT (Arm B- experimental arm). Surgery is carried out as gastrectomy or transhiatal extended gastrectomy. Primary endpoint is PFS/DFS, major secondary endpoints are OS, R0 resection rate, perioperative morbidity/mortality including VAS pain score and quality of life as assessed by EORTC QLQ C30 questionnaire. The trial starts with a safety run-in phase. After 20 patients had curatively intended resection in Arm B, an interim safety analysis is performed assessing feasibility, safety, and tolerability in Arm B. First patient was randomized on 18JAN2021. Currently one patient is recruited. EudraCT: 2017-003832-35; ClinicalTrials.gov ID: NCT04447352. Clinical trial information: NCT04447352