The purpose of this study was to evaluate the prognostic significance of CD8+ T cell and macrophage peritumoral infiltration in patients with colorectal cancer. A total of 97 adenocarcinomas of the colon and rectum were examined. Immunohistochemical staining was performed by the standard avidin-biotin-peroxidase complex method using antibodies to CD8 and CD68. Peritumoral infiltration by CD8+ T cells or macrophages was evaluated along the invasive margin of the cancer in each specimen. The area with the most abundant infiltration was selected, and the number of immunoreactive positive cells counted at x400 magnification. Patients were divided into two groups based on the degree of infiltration by each cell type: namely those with a high level of infiltration (more than the mean number of positive cells) and those with a low level of infiltration (less than the mean number of positive cells). Patients with a low level of macrophage infiltration had a significantly deeper depth of invasion than patients with a high level of macrophage infiltration (P=0.027). The percentage of patients with a high level of macrophage infiltration was significantly higher in vascular invasion-negative cases (46.7%) than in vascular invasion-positive cases (22.7%; P=0.045), and in lymph node metastasis-negative cases (52.9%) than in lymph node metastasis-positive cases (28.3%; P=0.014). Overall survival was significantly shorter for patients with a low level of CD8+ T cell infiltration than those with a high level of CD8+ T cell infiltration (P=0.01). The survival rate for patients with a high level of both CD8+ T cell and macrophage infiltration was 100%. In conclusion, both CD8+ T cell and macrophage peritumoral infiltration indicates anti-tumoral action in patients with colorectal cancer.

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