Macrophage polarization is relevant for tumor biology. M2 polarized macrophages favor tumor growth and survival, while M1 macrophages support tumor destruction and antigen presentation. Markers identifying M1/M2 polarization are a subject of debate. We conducted a systematic review and meta-analysis to investigate the association of proposed macrophage markers with prognosis across epithelial tumors and melanoma. The Medline search engine was used and 195 articles were recovered for full review. Only articles which measured markers using immunohistochemistry or immunofluorescence and had overall survival (OS) as the primary endpoint were included. One hundred and thirteen articles were finally accepted for analysis. CD68 was associated with worse survival across tumors (hazard ratio (HR) = 1.24, 95% CI = 1.11–1.37). Tumor anatomical location influenced this association. Colorectal tumors showed an inverse association between CD68 and OS in contrast to the rest of cancer types (HR = 0.56 vs. 1.34). The approach taken to measure CD68 had an impact on prognosis; when macrophages were measured at the tumor invasion front prognosis was more favorable than when they were measured intratumorally (HR = 0.94 vs. 1.4). CD163, CD204, and CD206 showed a robust association with worse OS (HR = 1.63, 1.95, 1.65, respectively). Tumors arising in the lung and the liver showed a weaker association between CD163 and OS as compared with other locations (β = −0.5401 for the lung and −0.5940 for the liver compared with other anatomical locations). The counting strategy also had an impact on CD163 association with OS, with hot-spot counting having higher HRs compared with averaging macrophage counts across spots or absolute cell counting (β = −0.4678). In conclusion, proposed M2 markers are associated with worse survival across epithelial tumors and melanoma. The anatomical origin of tumors influences this association. The compartment where the macrophages were scored and counting strategy influenced the association with OS of CD68 and CD163, respectively.
