PIK3CA and breast cancer: In particular, TP53 was mutated in 27% of HR+/HER2− metastatic breast cancer (mBC) as compared to 20% in HR+/HER2− early breast cancer (eBC) (Fisher Exact Test p = 0.13) while PIK3CA was mutated in 37% of the HR+/HER2− mBC and in 40% in eBC.