ESR1 and breast cancer: Although anti-miR-196a inhibitor reduced cell proliferation in both MCF7 and MDA-MB-231 cells without E2 stimulation, the anti-miR-196a inhibitor reversed the E2-promoted cell proliferation of only the ER+ BC cells MCF7, but not of ER- BC cells MDA-MB-231 (Fig. 2a and b).