For instance, as monotherapy, mifepristone was demonstrated to block the proliferation of breast cancer cells carrying PR and ER, such as T-47D and MCF-7 cells in the absence or presence of estrogens (Bardon et al. 1985, Horwitz 1985, Gill et al. 1987, Musgrove et al. 1997). The gene discussed is ESR1; the disease is breast cancer.