The peripheral monocyte count is associated with the density of tumor-associated macrophages in the tumor microenvironment of colorectal cancer: a retrospective study

BACKGROUND: Inflammation is widely recognized to play an important role in cancer progression, and the peripheral monocyte count has been reported to correlate with the prognosis in patients with colorectal cancer. This is based on the hypothesis that the peripheral monocyte level and the density of tumor-associated macrophages (TAMs) in the cancer microenvironment correlate with each other. However, the influence of TAMs on the prognosis and the correlation between the peripheral monocyte count and the density of TAMs have not yet been elucidated. METHODS: A total of 168 patients with stage II/III colorectal cancer were enrolled in this study. Preoperative blood samples were obtained at the time of the diagnosis before surgery. The expression of TAMs in the cancer microenvironment was assessed by immunohistochemistry. RESULTS: The progression-free and overall survival rate were significantly worse in the high-TAMs group than in the low-TAMs group (p = 0.0012 and p = 0.0207, respectively). The peripheral monocyte count was significantly associated with the number of TAMs (correlation coefficients: 0.202, p = 0.047). CONCLUSIONS: The peripheral monocyte count was associated with the density of the TAMs, which created a microenvironment favorable for cancer development and were correlated with a poor prognosis. Therefore, the peripheral monocyte count is a useful prognostic marker reflecting the status of the tumor microenvironment.