PIK3CA and neoplasm: PIK3CA activating tumor mutations may occur in several domains of the p110α catalytic subunit, but mostly (≈80%) arise in four hotspots of the helical and kinase domains: E542K, E545K, H1047R, and H1047L (Zhao and Vogt, 2008; Kalinsky et al., 2009; Dogruluk et al., 2015).