As many data suggest that luminal and non-luminal HER2 positive breast cancers are different entities with regard to their biology and response to therapies [11, 12] and hormonal receptors are important targets also in HER2-positive cancers, efficacy of the combination of endocrine therapies (ET) with HER2 directed agents was an obvious and relevant question to ask in clinical trials addressing this population. This evidence concerns the gene ERBB2 and breast cancer.