Mutant genes in tumor tissues are significantly associated with various cancer types, such as endometrial, pancreatic, hepatocellular, breast, colorectal, and gastric cancers, as well as the phosphatidylinositol 3-kinase–protein kinase B (PI3K–Akt) signaling pathway, which is a major signaling pathway in cancer. The gene discussed is PIK3CA; the disease is cancer.