Based on the subtype-specific impact of TP53 and PIK3CA mutations, and of p53 protein expression, multivariate analyses were performed in the three major subsets of breast cancer patients, i.e., Luminal A/B, TNBC and HER2-positive, the latter in the pre- and post-trastuzumab era. This evidence concerns the gene ERBB2 and breast carcinoma.