There are five molecular subtypes of BC which differ in their molecular presentation: luminal A (hormone receptor (HR)+, HER2–), luminal B (HR+, HER2–/+), triple-negative (HR–, HER2–), HER2-enriched (HR–, HER2+), and normal-like, which is similar to luminal A. Triple-negative breast cancer can be further classified into basal-like 1, basal-like 2, immunomodulatory, mesenchymal, mesenchymal-stem like, luminal androgen receptor, or unstable. The gene discussed is ERBB2; the disease is breast carcinoma.