Four clinical subtypes of breast cancer can be separated according to HR expression and the epithelial cell of origin (luminal or basal): Luminal A (HR+/Her2-), Luminal B (HR+/Her2+), Her2-enriched (HR-/Her2+), and triple-negative (HR-/Her2-) [4–7]. The gene discussed is ERBB2; the disease is breast carcinoma.