PIK3CA (phosphatidylinositol 3-kinase catalytic subunit, PI3K) is the catalytic subunit of a heterodimeric lipid kinase that is a member of a family that regulates cell growth, transformation, adhesion, apoptosis, survival and motility. Activation of PIK3CA by a growth factor bound receptor tyrosine kinase and downstream production of PIP3 drives pathways that are involved in tumor development and progression in a variety of cancers. PIK3CA kinase is frequently mutated or amplified in cancer, and gene amplifications, deletions and more recently, somatic missense mutations in the PIK3CA gene have been reported in many human cancer types including cancers of the colon, breast, brain, liver, stomach, cervix and lung. Staining is expected to be primarily cytoplasmic but may also localize to cell membranes. PIK3CA is widely expressed in normal tissues. References: Br. J. Cancer 2006 94(4):455; Rosty, 2013; Chang, 2016; Xu, 2017; Oncogene 2000 19:2739