Breast cancer can be classified according to three cellular markers: (i) progesterone receptor (PR) or estrogen receptor (ER) positive, (ii) human epidermal growth factor receptor-2 (HER2) positive, and PR and/or ER positive or negative, and (iii) triple negative breast cancer (TNBC) [2,3,4]. This evidence concerns the gene ERBB2 and breast cancer.