ERBB2 and breast cancer: In order to predict recurrence and mortality of breast cancer, previous studies stratified patients into high‐ and low‐risk groups based on their histopathological features, including tumour size, lymph node status and grade.5 While because of molecular differences, clinical outcomes are largely different even in patients with histologically similar tumours.6 During the past decade, molecular studies demonstrated that there were at least four molecular subtypes of breast cancer: luminal, basal, human epidermal growth factor receptor 2 (HER2)‐enriched and normal‐like.