Correlations of Tumor-associated Macrophage Subtypes with Liver Metastases of Colorectal Cancer

Objective: This work aimed to investigate the correlations of tumor-associated macrophages (TAMs) and their subtypes M1 and M2 with liver metastasis of colorectal cancer, and provide useful references for seeking predictors of liver metastasis and studying mechanisms. Methods: 120 patients with colorectal cancer from 2000 to 2009 were divided into low, middle and high liver metastasis groups (group A, B and C, respectively). S-P immunohistochemical staining and microscopic observation were conducted to compare expression in CD68-positive cells (TAMs), CD80-positive cells (M1) and CD163-positive cells (M2) in three groups. Correlations of TAMs, M1, M2, and M2/M1 ratio with clinical and pathological parameters were analyzed. Results: With increase of liver metastatic ability, the number of TAMs decreased gradually, with no significant difference between any two of the three groups (P > 0.05), while the numbers of M1 and M2 were significantly decreased and increased, respectively, with significant difference between any two of three groups (P < 0.05 or P < 0.01). In addition, the M2/M1 ratio increased with increase of liver metastatic ability (P < 0.01). There was no statistical significance of correlation of TAMs with each clinical and pathological parameter. M1 was negatively related with lymphatic metastasis and liver metastatic ability. M2 was positively correlated with preoperative CEA level, lymphatic metastasis, tumor differentiation degree and liver metastatic ability. The same was the case for the M2/M1 ratio. Conclusions: Effects of TAMs on liver metastasis of colorectal cancer do not depend on the total number of TAMs, but on the number and proportion of functional subtypes M1 and M2. M2 number and M2/M1 ratio are more accurate predictors for liver metastasis of colorectal cancer.