Fulvestrant, a selective estrogen receptor down-regulator, sensitizes estrogen receptor negative breast tumors to chemotherapy

Drug resistance frequently results in poor prognosis and high 5-year recurrence rate in estrogen receptor-negative (ER−) breast cancer patients. Herein, we examined the reversal effects of fulvestrant on multidrug resistance (MDR) in ER− breast cancer cells. Co-administration of fulvestrant significantly sensitized ER− MDR tumors to paclitaxel both in vitro and in vivo. Further analyses indicated that fulvestrant did not affect P-gp expression, but could inhibit P-gp function and subsequently reverse P-gp mediated drug resistance in ER− breast cancer cells. These results showed that combination of fulvestrant and chemotherapeutic agents might provide an effective treatment for ER− MDR breast cancers.