In conclusion, we thoroughly overviewed the current knowledge about the mechanisms of pituitary tumorigenesis, including the somatic and rarer germline mutations, in the genes pre-disposed to pituitary adenomas, as well as some the crucial molecules involving the MAPK and PI3K/Akt signaling, Wnt pathway, and lately the Hippo pathway. The gene discussed is PIK3CA; the disease is pituitary gland adenoma.