Tumor-associated macrophages are strongly related to vascular invasion, non-luminal subtypes, and interval breast cancer.

Tumor-associated macrophages (TAM) resemble M2 macrophages, promote tumor invasion and show strong expression of CD163 in breast cancer. We here investigated the association between CD163-positive macrophages and vascular invasion, molecular subgroups, mode of detection, and patient outcome. We performed a population-based, retrospective study of invasive breast cancer from the Norwegian Breast Cancer Screening Programme in Vestfold County (2004-2009), including 200 screen-detected and 82 interval cancers. Immunohistochemically CD163-positive macrophages were counted in the most active areas (hotspots) and dichotomized as high (upper quartile) and low counts. Lymphatic vessel involvement (LVI) and blood vessel invasion (BVI) were recorded separately based on immunohistochemical staining (D2-40 and CD31 antibodies). High levels of CD163-positive macrophages were associated with BVI and lymphatic involvement as well as interval cancer detection when compared to screening-detected tumors. In addition, the presence of high CD163+ TAM levels was more often observed in HER2-positive, basal-like and Triple-negative breast cancers and was associated with several features of aggressive tumors. In survival analyses, cases with combined high CD163 counts and BVI showed a significantly reduced recurrence-free survival (RFS) and disease-specific survival (DSS) (P < .001 for both) compared with all other cases. The presence of CD163-positive, tumor-associated macrophages is strongly related to aggressive features of breast cancer such as vessel invasion, detection between screening intervals, non-luminal molecular subgroups and reduced survival.