PIK3CD and cancer: Mutation of PIK3CA—the gene that encodes PI3K subunit p110α—drives cancer cell proliferation,23 whereas several reports support the hypothesis that PIK3CB is responsible for driving tumourigenesis in the absence of mutations and specifically in the context of tumors that contain wild-type PIK3CA and have lost functional PTEN.16,17 However, more recently, somatic mutations in PIK3CB have been identified in patients with cancers from a diverse range of lineages, including prostate, esophageal and renal carcinoma.18,22,24