ABCB1 and breast cancer: The MCF-7/KCR cells utilized in the previous work were evolved from MCF-7 breast cancer cells under gradually increasing concentrations of Doxorubicin and were shown to overexpress mainly just ABCB1 (P-glycoprotein), and therefore, MCF-7/KCR cells represent a MDR cancer cell model, where drug resistance is acquired due to drug selection pressure.