Furthermore, this observation is not only evident with targeted EGFR and ERBB2 RTKs but also with pan-ERBB inhibitors, such as AZD8931, in which a recent phase II randomised study in combination with an AI in women with endocrine-naive advanced BC provided no benefit compared with anastrozole alone and did not delay endocrine resistance in this patient population [27]. This evidence concerns the gene ERBB2 and breast cancer.