FLT1 and neoplasm: The VEGF-A receptor VEGFR-1 has been shown to be expressed in several components of the tumour microenvironment, besides tumour cells themselves: tumour infiltrating endothelial cells, and tumour-associated macrophages of the pro-tumour M2 phenotype, whose precursors are mobilized from the bone marrow and recruited to the tumour site through VEGFR-1 activation by specific ligands.