ESR1 and breast cancer: Cryptotanshinone could lead to the apoptosis of MCF-7 cells as a potent stimulator of ER stress mediated by mitogen-activated protein kinases (Park I. J. et al., 2012), and inhibit the growth of ERα-positive breast cancer cells by competitively binding to ERα to suppress ER transcriptional activity (Li et al., 2015).