ABCG2 and breast cancer: In contrast, in the group with tumor responses, we found a statistically significant down-regulation of expression of ABCB1, ABCC1, ABCC2, ABCC5, ABCG1, ABCG2 and MVP genes following chemotherapy in breast cancer patients [6], and a decrease in MDR protein expression was revealed by Kim et al. (2013) [18].