Tumor-associated macrophage (TAM) infiltration in gastric cancer

Background: Tumor-associated macrophages (TAMs) are defined as macrophages that migrate into the tumor stroma. TAMs are known to directly or indirectly affect immune suppression. TAMs have not previously been reported in gastric cancer. Materials and Methods: Using anti-CD68 antibodies, we immunohistochemically evaluated TAM infiltration in 97 gastric cancer patients who underwent tumor resection. Furthermore, CD3-zeta chain expression of tumor infiltrating lymphocytes (TILs) from the same section was also examined. According to the degree of TAM infiltration, 97 patients were divided into two groups (high TAM group, more than 200 positive cells; low TAM group, less than 200 positive cells). Clarification of the clinicopathological features of TAM-positive gastric cancer was attempted. Results: TAM infiltration in the tumor nest ranged from 0 to 621 cells (average 187). The degree of infiltration positively correlated with depth of invasion, nodal status and clinical stage. Patients in the high TAM group had lower CD3-zeta expression by TILs than patients in the low TAM group. CD3-zeta expression by TILs negatively con-elated with infiltration of TAMs (p<0.01). Patients with a high TAM count had poorer surgical outcomes than those with a low TAM count. Conclusion: From the results of the current study, TAM infiltration may be used as a prognostic marker in gastric cancer. Negative correlation between TAM infiltration and CD3-zeta expression by TILs suggests that TAMs may be responsible for the immunological inactivity of T cells in gastric cancer.