According to the recommendations from the College of American Pathologists and the American Society of Clinical Oncology (CAP/ASCO)3, a tumour is determined as HER2 positive if the number of tumour cells displaying strong HER2 overexpression (3+ cells) exceeds 10% of the total tumour population; equivocal if the number of tumour cells displaying moderate HER2 overexpression (2+ cells) exceeds 10% of the total tumour population and negative otherwise (Fig. 1). Here, ERBB2 is linked to neoplasm.