HRAS encodes transforming protein 21, which has intrinsic GTPase activity. HRAS activation by growth factors stimulates multiple effector pathways such as RAF and PI3K to promote cell proliferation. Simple variants in HRAS are seen in about 2.4% of all tumors, including 12% of salivary gland tumors and 11% of skin tumors. HRAS mutations may indicate possible treatment with MEK pathway and PI3K pathway inhibitors.