ERBB2 and breast cancer: Four breast cancer subtypes are luminal A (ER+, PR+/−, HER-2−), luminal B (ER+, PR+/−, HER-2+), HER-2-enrich (ER−, PR−, HER-2+), and basal-like (ER−, PR−, HER-2−), triple negative (TN).