Signing the informed consent to participate in the study. All the patients with suspected peritoneal carcinomatosis (according to the results of radiation diagnostics, as well as confirmed peritoneal carcinomatosis by puncture biopsy or by taking ascitic fluid) undergo diagnostic laparoscopy at the first stage. In addition, screening will include all the patients with locally advanced gastric cancer undergoing laparoscopy prior to planning combination treatment. If they have foci of carcinomatosis in the peritoneum PCI up to 15 inclusive and/or Cy+ (as the only manifestation of M1), the patients of this group can be included in the study. The methodology for performing diagnostic laparoscopy is described below (excluding dPIPAC components). Note - the examination of the omental bursa as part of diagnostic laparoscopy is optional, depending on the clinical situation. Screening and examination of patients according to current clinical guidelines for nosology stomach cancer taking into account the examination criteria specified in this protocol. Performing initial diagnostic laparoscopy at the stationary stage according to the standard procedure (described above). If carcinomatosis is detected the evaluation of PCI is carried out by Sugarbaker. The patient randomization based on positive (Cy+) abdominal flushing and/or peritoneal dissemination with PCI index \<16. The randomization will be carried out using an Internet resource https://www.sealedenvelope.com. Taking into account the planned set and heterogeneity of the groups, the patients will be stratified before randomization according to the following factors: microscopic carcinomatosis of Cy+ only, macroscopic carcinomatosis PCI up to 7 inclusive, macroscopic carcinomatosis PCI from 8 to 15 inclusive; accordingly, the patients within the strata will be randomized separately.

The Control group (the group No 1). Within 1-4 weeks after the initial diagnostic laparoscopy the group No 1 patients start polychemotherapy courses according to the FLOT scheme in the amount of 6 (six); the examination is carried out every 3 courses (after the 3rd and the 6th courses) with the control diagnostic laparoscopy after 6 courses of polychemotherapy for no more than 2 weeks with no obvious signs of progression (in this case, the patient switches to the 2nd line of chemotherapy). The evaluation of the therapeutic pathomorphosis of foci in the peritoneum is carried out according to the PRGS system (Peritoneal Regression Grading Score). As the result of the treatment: in the event of the complete regression of foci along the peritoneum and receiving Cy- in the peritoneal lavage, after the completion of the planned treatment, the patients switch to the dynamic observation or cytoreductive surgery is considered within 1 month after the completion of polychemotherapy (optionally, by decision of the local council); in case of the incomplete response (due to the immeasurable characteristics of the tumor and the impossibility of evaluation by RECIST), the dynamic observation is carried out until progression; in case of progression the 2nd line of chemotherapy (the scheme at the discretion of the attending physician) or the optimal palliative care options depending on the clinical situation is considered; accordingly the patient completes the therapy proposed by the study. The response criteria are specified separately. Shifting the timing of chemotherapy up to 10 days and the timing of control examinations up to 10 days due to objective circumstances is considered acceptable within the study.

The Study group (the group No 2). Within 1-4 weeks after the initial diagnostic laparoscopy the group No 2 patients start polychemotherapy courses according to the scheme FLOT (the 1st , the 3rd, the 5th courses) and mFLOT (the 2nd, the 4th, the 6th courses) in the amount of 6 (six, 3+3); the examination is carried out every 3 courses (after the 3rd and the 6th courses) with with dPIPAC sessions using docetaxel the examination is carried out every 3 courses (after the 3rd and 6th) with the performance of dPIPAC sessions using docetaxel (thus excluding it from the system administration) in the 2nd , the 4th, the 6th courses of polychemotherapy (all the procedures are performed according to the method described in the protocol; the evaluation of the therapeutic pathomorphosis of lesions in the peritoneum is carried out according to the PRGS system (Peritoneal Regression Grading Score)). Control diagnostic laparoscopy is not performed in the group No 2, its function is performed by the revision at the PIPAC session of the 6th course of polychemotherapy, which corresponds to the time interval of the group No 1. As the result of the treatment: in the event of the complete regression of foci along the peritoneum and receiving Cy- in the peritoneal lavage, after the completion of the planned treatment, the patients switch to the dynamic observation or cytoreductive surgery is considered after the completion of polychemotherapy (optionally, by decision of the local council); in case of the incomplete response (due to the immeasurable characteristics of the tumor and the impossibility of evaluation by RECIST), the dynamic observation is carried out until progression; in case of progression the 2nd line of chemotherapy (the scheme at the discretion of the attending physician) or the optimal palliative care options depending on the clinical situation is considered; accordingly the patient completes the therapy proposed by the study. The method of performing the surgical manual is specified separately. The response criteria are specified separately. Shifting the timing of chemotherapy with dPIPAC sessions up to 10 days and the timing of control examinations up to 10 days due to objective circumstances is considered acceptable within the study.