MAPK3 and neoplasm: In the past, VEGFR1 was less frequently investigated because it was not considered to be a signaling receptor or mediator of traditional VEGF-associated functions in endothelial cells.[20] In 2005, Wey et al[21] demonstrated that VEGFR1 could activate the extracellular regulated protein kinases (ERK1/2) signaling pathway to promote tumor cell migration and invasion in pancreatic carcinoma cell lines.