Objective: There is heterogeneity in the prognosis of gastric cancers staged according to the tumornodes-metastasis(TNM) system.This study evaluated the prognostic potential of an immune score system to supplement the TNM staging system.Methods: An immunohistochemical analysis was conducted to assess the density of T cells, B cells, and myeloid-derived suppressor cells(MDSCs) in cancer tissues from 100 stage ⅢA gastric cancer patients; the expression of the high-mobility group protein B1(HMGB1) was also evaluated in cancer cells.The relationship between the overall survival(OS), disease-free survival(DFS), and immunological parameters was analyzed.Results: An immune score system was compiled based on the prognostic role of the density of T cells, B cells, MDSCs, and the expression of HMGB1 in cancer tissues.The median 5-year survival of this group of patient was 32%.However, the 5-year survival rates of 80.0%, 51.7%, 0%, 5.8%, and 0% varied among the patients with an immune score of 4 to those with an immune score of 0 based on the immune score system, respectively.Similarly, differences in DFS rates were observed among the immune score subgroups.Conclusions: An immune score system could effectively identify the prognostic heterogeneity within stage ⅢA gastric cancer patients, implying that this immune score system may potentially supplement the TNM staging system, and help in identifying a more homogeneous group of patients who on the basis of prognosis can undergo adjuvant therapy. Objective: There is heterogeneity in the prognosis of gastric cancers staged according to the tumornodes-metastasis (TNM) system. This study evaluated the prognostic potential of an immune score system to supplement the TNM staging system. Methods: An immunohistochemical analysis was conducted to assess the density of T cells, B cells, and myeloid-derived suppressor cells (MDSCs) in cancer tissues from 100 stage III A gastric cancer patients; the expression of the high-mobility group protein B1 (HMGB1) was also evaluated in cancer cells. relationship between the overall survival (OS), disease-free survival (DFS), and immunological parameters were analyzed. Results: An immune score system was compiled based on the prognostic role of the density of T cells, B cells, MDSCs, and the expression of HMGB1 in cancer tissues. The median 5-year survival of this group of patients was 32% .However, the 5-year survival rates of 80.0%, 51.7%, 0%, 5.8%, and 0% varied among the patients with an immune score of 4 to those with an immune score of 0 based on the immune score system, respectively.Similarly, differences in DFS rates were observed among the immune score subgroups.Conclusions: An immune score system could effectively identify the prognostic heterogeneity within stage IIIA gastric cancer patients implying that this immune score system may potentially supplement the TNM staging system, and help in identifying a more homogeneous group of patients who on the basis of prognosis can be able to adjuvant therapy.