Abstract: Background and purpose: Breast cancer has the highest morbidity and mortality rate in women worldwide. Triple-negative breast cancer (TNBC) has no specific target and has low survival rate. Recent studies have verified BRD4 could promote tumor progression. This study aimed to detect the expression level of BRD4 in TNBC after treatment with gemcitabine, and to reveal the effect of BRD4 silencing plus gemcitabine as a treatment for TNBC. Methods: The expression of BRD4 in TNBC cell lines treated with gemcitabine was detected by reverse transcription PCR (RT-PCR) and Western blot. The effect of BRD4 silencing plus gemcitabine in TNBC was illustrated in vitro and in vivo. Results: The expression of BRD4 in TNBC was significantly increased after treatment with gemcitabine. In vitro, BRD4 knockdown significantly lowered the IC50 value. The apoptotic rate of TNBC was significantly increased in the BRD4 silencing plus gemcitabine group compared to the other. The growth rate of tumor in vivo was significantly lowered in the BRD4 silencing plus gemcitabine group. Conclusion: BRD4 may play an important role in the drug resistance to gemcitabine in TNBC. BRD4 silencing plus gemcitabine may be a novel treatment strategy for TNBC.

Key words: Triple-negative breast cancer, BRD4, Gemcitabine