Figure 7A shows that the number of colonies formed by MDA-MB-231 cells in the miR-186-5p mimic group was significantly reduced than the miR-186-5p mimic NC group, suggesting that miR-186-5p could inhibit the proliferation ability of cancer cells. After adding 740Y-P, the number of colonies formed by MDA-MB-231 cells was not significantly changed. Meanwhile, the results were consistent with Western blotting, the expression of Cyclin D1, PCNA and Cyclin B1 proteins in MDA-MB-231 cells was significantly reduced in miR-186-5p mimic group than in miR-186-5p mimic NC group (Figure 7B). This evidence concerns the gene CCNB1 and cancer.