Sorafenib is an inhibitor of wild-type and mutant proto-oncogene BRaf (B-Raf) and proto-oncogene c-Raf (c-Raf) kinase isoforms in vitro, but it also inhibits mitogen-activated protein kinase (p38), proto-oncogene c-kit (c-kit), vascular endothelial growth factor receptor 2 (VEGFR-2) and platelet-derived growth factor (PDGFR)-Beta affecting tumor growth as well as possibly promoting apoptosis by events downstream of c-Raf.