Phenotypical change of tumor-associated macrophages in metastatic lesions of clear cell renal cell carcinoma

Macrophages are the main immune cells of the tumor microenvironment in clear cell renal cell carcinoma (ccRCC). A high density of CD163+ or CD204+ tumor-associated macrophages (TAMs), rather than the density of total TAMs, is known to be linked to poor clinical outcome. In the present study, we investigated the phenotypical differences between the paired primary and metastatic lesions in ccRCC cases. Using immunostaining, the densities of CD163+ and CD204+ TAMs in metastatic lesions were found to be significantly lower compared to primary lesions, although the total number of TAMs was increased in metastatic lesions. Since CD163 and CD204 are considered to be the markers of an M2/protumor phenotype in macrophages, TAMs in metastatic lesions are suggested to have a greater M1/inflammatory function compared with those from primary lesions. These findings give new insights in regard to the immunological status of metastatic lesions of ccRCC.