The breast cancer is currently classified into four different molecular subtypes: Hormone receptor (HR)(+)/HER2(−) [Luminal A], HR(+)/HER2(+) [Luminal B], HR(−)/HER2(+) [HER2-enriched] and HR(−)/HER2(−) [triple negative or basal-like] [23,24,25,26,27]. The gene discussed is ERBB2; the disease is breast cancer.