Importantly, we also showed that while tamoxifen further expanded the CD44+/CD24−/low population to 0.32% in MCF-7 mammospheres, AF reduced the CSC population back to 0.02%, which is the same proportion as that found within untreated MCF-7 monolayers.13 In this study, we sought to first determine whether miR125b-2–3p regulates CSC potential in MCF-7 cells and whether AF must induce miR125b-2–3p to decrease mammospheres derived from luminal BC cells. The gene discussed is CD44; the disease is atrial fibrillation.