Because ARID1A down‐regulation in paclitaxel‐resistant cells and alteration upon paclitaxel treatment is more dominant than VMP1/MIR21, we next validated the correlation between endogenous ARID1A levels and paclitaxel IC50 concentrations in a panel of breast cancer cell lines and thereafter determined the clinical relevance of ARID1A in patients with breast cancer. This evidence concerns the gene MIR21 and breast cancer.