PIK3CA and breast cancer: Up to 44 % of all breast cancer subtypes bear PI3K pathway aberrations such as PIK3CA, PIK3R1, AKT1, and PTEN mutations, in particular luminal A (53.4 %) and ERBB2-enriched (47 %) subtypes, although much less common in the basal-like (10 %) subtype [83].