ESR1 and prostate cancer: For example, AR mutations or gene amplifications can confer resistance to antiandrogen therapy in prostate cancer, including Enz (Balbas et al., 2013; Joseph et al., 2013; Watson et al., 2015), and estrogen receptor (ER) mutations confer resistance to ER pathway therapies in breast cancer (Robinson et al., 2013; Toy et al., 2013; Jeselsohn et al., 2014).