Because knockdown of VEGFR1 has been shown to block macrophage recruitment into tumor tissues [73], and as our study shows that VEGFR1 is highly expressed on M1 but not on M2 macrophages, we speculate that high levels of VEGF produced by the decidual cells at the maternal-fetal interface may stimulate migration of M1 macrophages to this area and promote their differentiation into M2 macrophages. This evidence concerns the gene FLT1 and neoplasm.