Although our data, in general, did not reach statistical significance, it can be deduced that high BRK expression was significantly associated with poor RFS in tamoxifen-treatment patients (n = 161; P = 0.0043; Additional file 2: Figure S3G), thus strengthening the rationale for ER/BRK co-targeting in ER-positive breast cancers. This evidence concerns the gene ESR1 and breast cancer.