To determine whether there was an inverse correlation between MRP1 and miR-145 expression level in breast cancer, we tested the MRP1 and miR-145 expression level in two normal human mammary epithelial cell lines (MCF-10A and MDA-kb2) and four breast cancer lines (MCF-7, MDA-MB-231, MDA-MB-453 and MDA-MB-468); MCF-7 was used as a control cell line. The gene discussed is ABCC1; the disease is breast cancer.