PIK3CA and cancer: The most frequently mutated driver genes in BC are Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha (PIK3CA, coding for the α subunit of PI3K) in luminal A subtype (45%), PIK3CA and Tumor Protein P53 (TP53) in luminal B (29% each), TP53 in basal-like (80%), and TP53 and PIK3CA in HER2+ cancers (72% and 39%, respectively).