Notably, estrogen receptor (ER)-positive breast cancer cell lines, irrespective of resistance to anti-estrogen or anti-HER2 therapies (e.g., tamoxifen refractory MCF-7/TAM1 and herceptin refractory MCF-7/Her2-18 cell lines), were sensitive to AF, whereas triple-negative breast cancer cell (TNBC) lines with the molecular characteristics of basal B or mesenchymal-like subtypes (e.g., MDA-MB-231 and Hs578T) [12], [13] were resistant to AF [14]. This evidence concerns the gene ESR1 and atrial fibrillation.