ESR1 and breast cancer: Previous studies confirmed that WBP2 is a co-activator of ERα and WBP2 is conducive to the transcriptional activity of ERα through binding to ERα.24 Moreover, a previous report verified that ERα directly activated MDR1 transcription in PTX-induced resistance of ERα-positive breast cancer cells.15 Thus, we hypothesised that ERα was the key determinant that affected the expression pattern between WBP2 and MDR1 in breast cancer.