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The efficacy of cancer chemotherapy is limited by cellular mechanisms of resistance that result in increased drug efflux of chemotherapeutic agents thereby reducing intracellular drug levels and causing drug resistance. Overexpression of some members of ATP binding cassette transporter superfamily, including ATP binding cassette G member 2 (ABCG2), which mediates energy-dependent transport of drugs out of the cells against concentration gradient, is one of the major mechanisms responsible for multidrug resistance in the treatment of breast cancer. In the current study, the expression of ABCG2 mRNA gene was evaluated in the peripheral blood of newly diagnosed breast cancer (NDBC) patients immediately before surgical resection of the breast and in extirpated breast tumors, then sequentially in the blood of patients after receiving three and six cycles of chemotherapy. Compared to normal breast, cancerous specimens expressed higher levels of ABCG2 gene expression (p |
