PIK3CA and cancer: Besides the common alterations of the PIK3CA gene encoding the catalytic p110α subunit of class IA PI3K, somatic mutations in the PIK3R1 gene encoding the regulatory subunit p85α have been detected in multiple human cancers [41], including endometrium (26%), colon (5%), central nervous system (4%), breast (2%), pancreatic (2%), and skin (1%) (adapted from the COSMIC Database).