ESR1 and breast cancer: Studies on the role of p‐ERα(Ser118) in breast cancer patients treated with adjuvant tamoxifen were conflicting as some groups presented negative results,35, 36, 37 while others described that p‐ERα(Ser118) might predict response to endocrine therapy.17, 38 Expression of p‐ERα(Ser167) in primary tumors was predictive for response to endocrine therapy in the metastatic setting as reported by Yamashita et al. 37 Studies other than ours demonstrating an effect of p‐ERα(Ser167) on adjuvant endocrine therapy responses in patients are lacking.