KDR and neoplasm: Alternative exon splicing causes multiple isoforms of VEGF which are characterized by their differential ability to bind heparin.136 VEGF binds to both VEGF receptor 1 (R1) and VEGFR2 while VEGFR2 is the main receptor for VEGF.137,138 VEGF isoforms can also interact with the neuropilin co-receptors (NRP1 and NRP2).139,140 During tumorigenesis, angiogenesis plays a key role in maintaining the expansion in tumor.