The additional evaluation of the estrogen (ER) and progesterone (PR) hormone receptors coupled with human epidermal growth factor receptor 2 (HER2) categorizes BC into the following clinically relevant immunophenotypes: (i) luminal A (LUMA), (ii) luminal B (LUMB), (iii) triple-negative breast cancers (TNBC), and (iv) HER2-enriched (HER2+). This evidence concerns the gene ERBB2 and breast cancer.