ERBB2 and breast cancer: The clinical classification of BC is based on the expression of the oestrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), resulting in groups of hormone receptor‐positive (ER and PR positive), HER2‐positive and triple‐negative BC [triple‐negative breast cancer (TNBC); lacking ER and PR and without HER2 amplification] [2, 3, 4].