ERBB2 and breast cancer: Early breast cancer (eBC; stages 1–3) accounts for over 90% of newly-diagnosed cases of breast cancer within the UK, with human epidermal growth factor receptor 2 (HER2)-negative tumours accounting for 85% of eBC [1,2].a Despite this, there is currently no standardised UK definition of patients at ‘high risk’ of recurrence with HER2-negative eBC after surgery.