Although it is a heterogeneous disease, breast tumors can be classified based on the expression level of hormonal receptors for estrogen (ER), progesterone (PR), and human epidermal growth factor receptor 2 (HER2) in subtypes depending on the presence (+) or absence (–) of hormonal receptors, namely Luminal A (ER+, PR+/-, HER2-), Luminal B (ER+, PR+/-, HER2+), and HER2-enriched (ER -, PR -, HER2+). This evidence concerns the gene ERBB2 and breast neoplasm.