RET and neoplasm: Regorafenib is an oral inhibitor of several kinases involved in tumor angiogenesis (VEGFR1-3 and TIE2), oncogenesis (KIT, RET, RAF1, and BRAF), and in the interaction between tumor and microenvironment (PDGFR, FGFR), and tumor immunity (colony-stimulating factor 1 receptor [CSF1R]).