ERK1/2 is located downstream of the Raf/MEK/ERK (MAPK) signal transduction cascade, at which cancer signaling from various upstream growth factor receptors, such as ErbB/HER, VEGFR, PDGFR, c-kit, and hepatocyte growth factor receptor (Met), and from Ras, Raf, and MAPK/ERK kinase (MEK) signaling converge [4–7, 18–23]. Here, RAF1 is linked to cancer.