Despite the existence of well-established traditional prognostic markers, such as tumor size, patient age and menopausal status, tumor axillary lymph node involvement, lymphatic/vascular invasion status, hormone receptor status (estrogen (ER) and progesterone (PR)), status of human epidermal growth factor 2 receptor (HER2), and the pathologic prognostic stage (according to the AJCC Cancer Staging Manual, 8th edition [2]), clinical practice shows that, solely on the basis of these markers, it is not possible to identify the prognosis of all patients with BC reliably. This evidence concerns the gene ERBB2 and breast cancer.