Effect of overexpression or suppression of CDR1as on chemosensitivity of 5‐fluorouracil (5‐FU)‐resistant BC cells. (A) Expressions of CDR1as in BC cells and their corresponding 5‐FU‐resistant BC cells; (B), cell growth curve of 5‐FU‐resistant BC cells in each group after treatment by different concentration of 5‐Fu; (C), IC50 of 5‐FU‐resistant BC cells in each group; (D), colon formation images of 5‐FU‐resistant BC cells in each group by colon formation assay; (E), colon formation rate of 5‐FU‐resistant BC cells in each group; (F), cell apoptosis of 5‐FU‐resistant BC cells in each group; (G), cell apoptosis rate of 5‐FU‐resistant BC cells in each group; (H), Western blot on apoptosis related factors of 5‐FU‐resistant BC cells in each group; (I), expressions of apoptosis related factors of 5‐FU‐resistant BC cells in each group; *, compared with Blank group, P < 0.05; BC, breast cancer; IC50, half maximal inhibitory concentration