Even in early and non-invasive breast cancers (in situ carcinomas) in mice, CCL2-recruited tumor-infiltrating macrophages with pro-tumorigenic features (CD206+/Tie2+), downregulate expression of E-cadherin by malignant cells, thus destabilizing cell-cell junctions, which leads to cancer dissemination and metastasis. Here, MRC1 is linked to breast cancer.