RET and cancer: Sorafenib, a multi- kinase inhibitor (TKI), blocks cancer progression through inhibiting RAS-RAF-MEK-ERK-MAPK pathway, which relates to the proliferation, migration and angiogenesis of cancer cells by targeting vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR), c-kit and a receptor tyrosine kinase called rearranged during transfection (RET) [11].