Breast cancer resistance protein (BCRP)-containing circulating microvesicles contribute to chemoresistance in breast cancer.

At present, one of the major problems of cancer therapy is drug resistance. Breast cancer resistance protein (BCRP), a marker of the multidrug-resistant phenotype, affects drug absorption, distribution, metabolism, and excretion in normal tissues. Meanwhile, extracellular vesicles (EVs) have attracted increasing attention as a medium of cell-to-cell communication. However, the association between BCRP and circulating EVs remains unclear. The present study demonstrated that patients who did not respond or had progressive/stable disease following chemotherapy had markedly higher BCRP levels compared to those that did not receive chemotherapy. Moreover, BCRP was upregulated at the mRNA and protein levels in tumor-derived circulating EVs from patients with a poor response to chemotherapy. Interestingly, the results also demonstrated that BCRP was co-expressed with MUC1, which is frequently expressed in breast cancer and is exported via EVs, and both BCRP and MUC1 were up-regulated after chemotherapy. In conclusion, the present study indicates that tumor-derived circulating EVs that carry BCRP may serve as a predictive biomarker of the response to chemotherapy for breast cancer. In addition, the results provide a window for individualized treatment to overcome resistance to chemotherapeutic drugs.