On the other hand, MCF-7 human breast cancer cells, which contain oestrogen and progesterone receptors, exposed to low doses of anthracyclines may develop multidrug resistance, which is associated with multidrug resistance protein 1 (MDR1), CD44st and nuclear factor kappa-B (NF-κB) messenger RNA (mRNA) and protein expression [27]. This evidence concerns the gene ABCB1 and breast cancer.