These studies have shown that the expression profiles of breast cancer display a systematic variation and allow classification of breast cancer into five main groups, two of them ER+ (oestrogen receptor positive)[luminal A and B] and three ER− (oestrogen receptor negative) groups [normal breast-like, ERBB2 (also known as HER2) and ‘basal-like’][1, 3]. Here, ERBB2 is linked to breast cancer.