Objective:To investigate the efficacy and safety of hyperthermic intraperitoneal chemotherapy combined with immune checkpoint inhibitors in treatment of gastric cancer with ascites.Methods:A retrospective case-control study was conducted. The clinical data of 39 gastric cancer patients with malignant ascites treated in Xi'an Third Hospital from May 2021 to June 2023 were retrospectively analyzed. All patients were divided into the routine group (18 cases) and the observation group (21 cases) according to different treatment methods. The patients in the routine group were treated with hyperthermic intraperitoneal chemotherapy combined with systemic intravenous chemotherapy; the patients in the observation group were treated with immune checkpoint inhibitors on the basis of hyperthermic intraperitoneal chemotherapy combined with systemic intravenous chemotherapy. The clinical efficacy, tumor marker levels, Karnofsky scores, and incidence of adverse reactions of both groups were compared. Kaplan-Meier method was used to analyze the overall survival (OS) of both groups.Results:There were 12 males (66.7%) and 6 females (33.3%) in the routine group, with the age of (57±13) years; 13 males (61.9%) and 8 females (38.1%) in the observation group, with the age of (59±12) years. After treatment, the serum carcinoembryonic antigen (CEA), carbohydrate 125 (CA125), carbohydrate 199 (CA199) levels in the 2 groups were lower than those before treatment, and the differences were statistically significant (all P < 0.05). After treatment, the serum CEA, CA125, CA199 levels in the observation group were lower than those in the routine group, and the differences were statistically significant (all P < 0.05). After treatment, Karnofsky scores in the observation group were higher than those before treatment [(78.6±7.5) scores vs. (69.5±8.9) scores], and Karnofsky scores in the observation group were higher than those in the routine group [(78.6±7.5) scores vs. (72.8±7.9) scores],and the differences were statistically significant ( t = -3.65, 2.33, all P < 0.05). The objective remission rate (ORR) was 55.6% (10/18) and 71.4%(15/21), respectively in the routine group and the observation group, and the difference was statistically significant ( χ2 = 9.24, P = 0.002). The median OS time was 38.97 months (95% CI: 34.99-42.95 months) and 23.62 months (95% CI: 18.49-28.74 months), respectively in the observation group and the routine group, and the difference was statistically significant ( χ2 = 3.88, P = 0.049). There was no statistically significant difference in the incidence of adverse events between the 2 groups (all P > 0.05). No serious treatment-related complications were found in the observation group. Conclusions:Hyperthermic intraperitoneal chemotherapy combined with immune checkpoint inhibitors shows a good therapeutic effect in the treatment of gastric cancer with ascites, and the adverse reactions are controllable.