The importance of ERα expression in conferring sensitivity of breast cancer cells to AF was further corroborated by evidence that stable transfection of ERα into mesenchymal-like TNBC MDA-MB-231 cells rendered the cells sensitive to AF [15], whereas transient knockdown of ERα in luminal-like breast cancer MCF-7 cells conferred resistance to AF. This evidence concerns the gene ESR1 and atrial fibrillation.