The main purpose of this study is to evaluate the role of the type of omentectomy (partial or total) in the treatment of Tis - T3 gastric cancer without serosal infiltration. The second purpose is to monitoring the blood levels of immunological factors (interleukins, T cell subtypes, etc.) pre-and postoperatively, depending on the type of omentectomy.

Gastric cancer is the second common tumor type. In 2020, the incidence of gastric cancer was over one million and caused about 770 000 tumor-associated deaths worldwide. Although the improvement of the perioperative oncological therapy is unquestionable, the major point of the treatment is radical surgical intervention. Laparoscopic technic is widespread in the treatment of gastric cancer, too. For the oncological radicality total or subtotal gastrectomy with D2 omentectomy is necessary, but the opinions are divided about the role of the omentectomy. Total omentectomy in laparoscopic operations takes more time and increases the postoperative morbidity, blood loss, and opportunity of the anastomosis insufficiency, and the incidence of the omental metastases is just between 3,8 - 5%. Based on this, many international guidelines allow partial omentectomy in early gastric cancer. At the same time, in advanced gastric neoplasm, the place of the partial omentectomy is still unclear.

With this prospective, randomized, multicentric study we plan to compare the total and partial omentectomy in the surgery of Tis - T3 gastric cancer with the analysis of the postoperative morbidity and mortality and long-term survival factors.

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) I-III., Karnofsky Performance Score (KPS) >60, Eastern Cooperative Oncology Group (ECOG) 0-1
• Tis-T3 gastric cancer without serosal infiltration and treated with the radical operation (R0; D2 lymphadenectomy, lymph nodes >16)
• clinical stadium: Tis-3; M0
• written informed consent provided
• good patient compliance
• no previous chemotherapy or irradiation

Exclusion Criteria:

• serosal infiltration and/or distant metastasis, omental infiltration, peritoneal carcinosis, positive abdominal cytological lavage
• organ transplantation and/or immunological disease and/or immunomodulation therapy
• another primary tumor
• decompensated chronic disease (for example: liver cirrhosis with ascites, kidney failure treated with hemodialysis, New York Heart Association (NYHA) IV. cardiac status, etc.)
• unsuccessful follow-up