Earlier studies demonstrated that in the estrogen receptor (ER)‐positive (MCF‐7) and ER‐negative (SKBr3) breast cancer cell lines, inclusion of G‐1 in the growth media inhibited cell proliferation and induced cell cycle arrest in the G2/M phase (Ribeiro, Santos, and Custódio 2017; Weißenborn et al. 2014). This evidence concerns the gene ESR1 and breast cancer.