BAX and breast cancer: In both MCF‐7/5‐Fu cells and MDA‐MB‐231/5‐Fu cells, the expressions of Bax/Bcl2 and cleaved‐Caspase‐3/Caspase‐3 in si‐CDR1a group were increased, while those in CDR1as group were suppressed when compared to those in Empty plasmid group, suggesting that suppression on CDR1as may increase chemosensitivity of 5‐FU‐resistant BC cells.