PGR and uterine corpus leiomyoma: Studies using PR antagonists, such as 6 and the investigational drug onapristone (8), indicated that PR antagonists might be effective not only for contraception and uterine fibroids but also for the treatment of endometriosis, breast cancer, ovarian cancer, uterine cancer, and some psychiatric disorders [21,22,23,24,25,26,27].