ESR1 and breast cancer: Further trastuzumab treatment induces the interaction between CBP and ERα which in turn enhances ERα transcriptional activity and expression of the ERα target gene, pS2. Furthermore, metastatic tissues from patients who had failed for trastuzumab therapy were pS2-positive providing the proof that trastuzumab treatment can benefit endocrine-resistant breast cancer patients with hormone therapy [88].