Evaluating different biological markers -including presenceor absence of hormone (i.e. estrogen or progesterone)receptors (named respectively HR+ or HR-) and excessivelevel of human epidermal growth factor receptor 2 (HER-2)- is the most applicable method for identifying the subtypeof the cancer (4), leading to classification of some distinctsubtypes of breast cancer: luminal A (HR+/HER-2-), triplenegative (HR-/HER-2-), luminal B (HR+/HER-2+) and HER-2-enriched (HR-/HER-2+) tumors (5). The gene discussed is ERBB2; the disease is breast cancer.