The classical, canonical MAPK signaling pathway is an evolutionarily conserved pathway that controls the growth and survival of a large group of human tumors where it is shown to have increased and sustainable activation. It is involved in the control of many fundamental cellular processes that include cell proliferation, survival, differentiation, apoptosis, motility and metabolism. It accomplishes this through the promotion of cell proliferation and preventing apoptosis. In a normal cell, the signaling pathway is initiated by the binding of a growth factor such as EGF, VEGF, PDGF, HGF, and FGF, to its respective receptor. This ligand binding activates the receptor tyrosine kinase (RTK) that results in its binding of Grb2 that binds to specific phosphorylated residues in the intracellular tail portion of the receptor. SOS binds to Grb2 to activate the small G-protein Ras by catalyzing the replacement of GDP to GTP. In its GTP-bound active state, Ras activates the kinase activity of the Ser/Thr kinase Raf (MAP Kinase Kinase Kinase). Raf then binds to and activates MEK (MAP Kinase Kinase) by phosphorylating it on the two residue motif. MEK, a dual kinase (a Ser/Thr and a Tyr kinase), phosphorylates and activates ERK on the TxY motif. The regulation of a large number of cellular processes are dependent upon the activation state of ERK, so the controlling of this pathway could have profound effects on various diseases. Many malignant cancers are characterized by the deregulation of the ERK signaling cascades. Cancerous cells do not respond to cell signaling that would normally result in cell cycle arrest or apoptosis (programmed cell death). In fact, constitutive ERK signaling contributes to the evolution of some of the most lethal forms of cancer. In some cancers, ERK is upregulated and results in the migration and invasion of the cancerous cells. Inhibition of the ERK expression reduces migration and invasion. Many tumors show an increase, sustained activation of this pathway. Cellular activities that MAPKs modulate include cell division, proliferation, survival, differentiation, apoptosis, motility and metabolism. This is one reason why the MAPK signaling pathway is a highly sought after anti-cancer drug target.