Activating mutations of PIK3CA (1.6–2%) and inactivating mutations of tuberous sclerosis 1 (TSC1) or TSC2 (3–8%), genes involved in the phosphatidylinositol-3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling pathway, are found in HCC. The gene discussed is MTOR; the disease is hepatocellular carcinoma.