They are divided into three main groups: hormone receptor-positive subtype, which includes tumors expressing ERα and/or PR, which are subclassified as luminal A or B depending on the percentage of Ki-67; HER2-positive tumors, defined by the presence of ERBB2/HER2 amplifications and loss of ERα expression; and triple-negative breast cancer (TNBC), characterized by the lack of expression of the aforementioned molecular markers [2] (Figure 2). The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.