An early example of the former came from multiphoton intravital imaging of a murine model of breast cancer, which showed epithelial expression of Csf1 promotes the infiltration of Csfr1+ macrophages, while macrophages act as a source of EGF, leading to a mutually reinforcing paracrine signaling loop of CSF-1 and EGF ligands between macrophages and tumor cells that drive tumor invasion and metastasis (97, 98). This evidence concerns the gene EGF and breast carcinoma.