Conventionally, based on the expression features of three representative receptors: estrogen receptor (ER), progesterone receptor (PR), and human epidermal receptor 2 (HER2), breast cancers have been classified into luminal A, luminal B, HER2-positive, and triple-negative breast cancer (TNBC) subtypes. The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.