We first evaluated the effects of different ASA concentrations (0.695, 1.39, 2.78, and 5.56 mM) and time of treatment (24, 48, and 72 h) on the viability of three human breast cancer cell lines: two estrogen receptor (ER)-positive, MCF-7 and T-47D (Figure 1A,B, respectively), and a triple-negative breast cancer cell line, MDA-MB-231 (Figure 1C,D). This evidence concerns the gene ESR1 and breast cancer.