PIK3CA and gastric cancer: Many gene mutations are served as prognostic biomarkers for cancers, such as tumor protein P53 (TP53), phosphatase and tensin homolog (PTEN), and RB transcriptional corepressor 1 (RB1) mutations in prostate cancer, and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA), Erb-B2 Receptor Tyrosine Kinase 2 (ERBB2), and KRAS proto-oncogene and GTPase (KRAS) mutations in gastric cancer, as well as E1A binding protein P300 (EP300) in bladder cancer [9–11].