The GNAS gene encodes the stimulatory G-alpha subunit of the heterotrimeric guanine nucleotide-binding protein (G-protein) membrane complex. Activating mutations in GNAS that have been linked to the endocrine hyperplasia of McCune-Albright syndrome have also been found in growth-hormone-secreting pituitary tumors. Point mutations in the GNAS gene, many of which involve the residues R201 and Q227, can lead to constitutive signaling activity, resulting in cellular proliferation and oncogenesis. Tumor types that have been found to harbor GNAS mutations include colon, parathyroid, and ovarian cancers, hepatocellular carcinoma, and pancreatic intraductal papillary mucinous neoplasms. The GNAS R201C mutation is known to be oncogenic.