Macrophages orchestrate breast cancer early dissemination and metastasis

Abstract

Cancer cell dissemination during very early stages of breast cancer proceeds through poorly understood mechanisms. Here we show, in a mouse model of HER2 ⁺ breast cancer, that a previously described sub-population of early-evolved cancer cells requires macrophages for early dissemination. Depletion of macrophages specifically during pre-malignant stages reduces early dissemination and also results in reduced metastatic burden at end stages of cancer progression. Mechanistically, we show that, in pre-malignant lesions, CCL2 produced by cancer cells and myeloid cells attracts CD206 ⁺/Tie2 ⁺ macrophages and induces Wnt-1 upregulation that in turn downregulates E-cadherin junctions in the HER2 ⁺ early cancer cells. We also observe macrophage-containing tumor microenvironments of metastasis structures in the pre-malignant lesions that can operate as portals for intravasation. These data support a causal role for macrophages in early dissemination that affects long-term metastasis development much later in cancer progression. A pilot analysis on human specimens revealed intra-epithelial macrophages and loss of E-cadherin junctions in ductal carcinoma in situ, supporting a potential clinical relevance.

Abstract

Early dissemination of cancer cells has been reported to occur in certain breast cancer models. Here the authors show that intra-epithelial macrophages in the early pre-cancer lesions drive early cancer cell dissemination through Wnt-1 secretion and that such events impact the later development of metastasis.