Our versions support that intra-epithelial macrophages in turn secrete Wnt-1 in response to CCL2 production by cancer cells and also other immune cells and thereby further cement an EMT-like response that is also stimulated by autocrine/paracrine production of other Wnt ligands8, 9 to drive early dissemination

Our versions support that intra-epithelial macrophages in turn secrete Wnt-1 in response to CCL2 production by cancer cells and also other immune cells and thereby further cement an EMT-like response that is also stimulated by autocrine/paracrine production of other Wnt ligands8, 9 to drive early dissemination. ductal carcinoma in situ, supporting a potential clinical relevance. Introduction The paradigm of cancer metastasis states that dissemination and metastasis occur when advanced aggressive tumors acquire invasive mechanisms. The finding that dissemination does not only occur from evolutionary late-stage invasive tumors has challenged the uniqueness of this model1. Large cohort patient studies2C5 and studies with spontaneous mouse tumor models6 showed that dissemination also occurs during early stages of cancer when lesions are diagnosed by light microscopy as pre-malignant or pre-invasive. In addition, cancer of unknown primary is a relatively frequent event in solid cancers where metastases develop without the presence of an obvious primary tumor mass that evolved to become invasive7. The early dissemination definition was refined by Husemann et al.6 when they showed that early disseminated cancer cells (DCCs) originate at times when lesions are only defined in situ by light RN486 microscopy (e.g., ductal carcinoma in situ (DCIS) in humans and mammary intra-epithelial neoplasia RN486 in mice), but dissemination occurs and early DCCs show few genetic aberrations. Following previous work6, we found that in MMTV-HER2 early lesions there is a sub-population of HER2+/P-p38lo/P-ATF2lo/TWISThi/E-cadherinlo disseminating cancer cells that reach distant organs and initiate metastasis8, 9. Our studies revealed that HER2+ early cancer cells deregulate mechanisms of motility and invasion activated during mammary tissue branching morphogenesis8, 9. The remarkable finding was that early DCCs are endowed with latent metastasis-initiating capacity8, 9. Women treated for DCIS can develop metastases without ever developing any subsequent local invasive breast cancer10C14. This might indicate that, albeit at low frequency, early DCCs can unpredictably form metastases in patients. Early dissemination is not a rarity of breast cancer models (MMTV-HER2 and MMTV-PyMT models6, 8, 9), as it also occurs in spontaneous mouse models of melanoma15 and pancreatic cancer16. The mechanistic analysis of early dissemination has been primarily early cancer cell-centric8, 9. Since early DCCs displayed fewer genetic alterations than the late DCC counterparts4, 6, 8, and the mechanism of dissemination resembled steps of mammary morphogenesis8, 9, we hypothesized that early dissemination might be driven by micro-environmental mechanisms that control epithelial cell motility and invasion during mammary tissue development17, 18. The mammary epithelium forms post-natally during adolescence in a process called branching morphogenesis where RN486 rapidly dividing epithelial cells elongate the terminal end bud into the fat pad and bifurcate into the ductal tree. Macrophages are key regulators of branching morphogenesis during mammary gland development19, 20, arguing Esr1 that normal mammary epithelial cells cooperate with these innate immune cells for invasive processes. These data led to the discovery of macrophages as powerful drivers of intravasation from invasive breast cancer tumors via the establishment of tumor microenvironments of metastasis (TMEM)21. This follows a streaming process where breast cancer cells recruit macrophages through colony-stimulating factor 1 (CSF1) production and then cancer cell motility is stimulated via macrophage-derived epidermal growth factor (EGF)22. Additionally, macrophages can induce an epithelial-to-mesenchymal transition (EMT) in malignant cells23, 24. Elegant studies by Pollard and colleagues25 [,26 have also shown that macrophages play key roles in the maintenance of lung metastasis. However, the role of macrophages in the process of dissemination during evolutionary early stages of breast cancer progression remained unexplored. Here we show that the branching morphogenesis program is altered by oncogenes early in cancer development. CD206hi macrophages in the mammary tissue are attracted by early cancer cells from the stroma into the epithelial layer of lesions defined as mammary intra-epithelial neoplasia in mice (similar to DCIS in humans)27. In the MMTV-HER2 model this process depends on HER2-NF-B-mediated induction of CCL2. Our data suggest that intra-epithelial macrophages respond to CCL2, which in turn can stimulate macrophages to produce Wnt-1, leading to disruption of E-cadherin junctions between.