Our previous work showed that in pulmonary foci from mouse models of metastatic breast cancer, expression of, the FMS-like tyrosine kinase 1 (FLT1, also known as Vascular Endothelial Growth Factor 1, VEGFR1), allows the identification of a particular population of macrophages (herein called metastasis-associated macrophages (MAMs)), that differ phenotypically and functionally from both tumor-associated-macrophages (TAMs) at the primary site and myeloid resident cells in the lung [13,14,15]. This evidence concerns the gene FLT1 and neoplasm.