The KRAS gene encodes the human cellular homolog of a transforming gene isolated from the Kirsten rat sarcoma virus. The RAS proteins are GDP/GTP-binding proteins that act as intracellular signal transducers. The most well-studied members of the RAS (derived from 'RAt Sarcoma' virus) gene family include KRAS, HRAS (190020), and NRAS (164790). These genes encode immunologically related proteins with a molecular mass of 21 kD and are homologs of rodent sarcoma virus genes that have transforming abilities. While these wildtype cellular proteins in humans play a vital role in normal tissue signaling, including proliferation, differentiation, and senescence, mutated genes are potent oncogenes that play a role in many human cancers (Weinberg, 1982; Kranenburg, 2005).