PIK3CA and neoplasm: In addition to the different mutation frequencies of PIK3CA among the cohorts, the most common tumor-associated PIK3CA mutations (those involving the helical domain (exon 9: c.1624G>A:p.Glu542Lys and c.1633G>A:p.Glu545Lys) or the kinase domain (exon 20: c.3140A>G:p.His1047Arg)) had significantly different frequencies among these cohorts.