Based on their hormonal receptor status, four principal molecular BC subtypes have been identified: luminal A (ER+, PR+, HER2−), luminal B (ER+, PR+, HER2+), HER2+ (ER−, PR−, HER2+), and triple-negative (TN) (ER−, PR−, HER2−). The gene discussed is ERBB2; the disease is breast cancer.