Effect of miR-638 on sensitivity of breast cancer cell lines to anticancer drugs or UV treatment. miR-638 expression in breast cancer cell lines transfected with miR-638 mimic or inhibitor compared to the mock control was examined by qRT-PCR (A). Twenty-four h after transfection of miR-638 mimic, miR-638 inhibitor or mock, cells were treated by UVC, cisplatin, 5-FU and epirubicin, respectively for 48 h. Cell sensitivity was measured by MTT assay. miR-638 expression significantly increased sensitivity to UV (B) and cisplatin (C) in TNBC cell lines, MDA-MB-231 and Hs578T, but reduced sensitivity in MCF-7 cells compared with the mock. miR-638 expression did not change the sensitivity to 5-FU (D) and epirubicin (E) in breast cancer cell lines. Results are displayed as mean data ± SE. *P <0.05, in comparison to the mock. 5-FU, 5-fluorouracil; TNBC, triple-negative breast cancer.