For instance, there has been a report of downregulation of ABCB1/MDR1 encoding for P-gp by several miRNAs such as miR-331-5p and miR-27a in lymphocytic and myeloid leukemia, miR-let-7 in ovarian cancer, miR-200c and miR-195 in breast cancer, miR-30a in gastric cancer and miR-9-3p in CML, thereby reversing the phenomenon of drug resistance [130–135]. This evidence concerns the gene ABCB1 and breast cancer.