FLT1 and neoplasm: Many factors, including VEGFs, PDGFs and their receptor tyrosine kinases (RTKs), VEGF receptors 1–3 (VEGFR1–3), and PDGF receptor-α and -β (PDGFR-α/β), participate in tumor-induced angiogenesis signaling pathways in the tumor microenviroment [4].