PGR and endometriosis: Although DNG has recently been launched for the treatment of endometriosis, DNG also has antiproliferative effects on estrogen receptosr (ERs)- and/or PR-positive endometrial and breast cancer cells in vitro, suggesting potential usefulness in the treatment of ER/PR-positive malignant tumors (Katsuki et al. 1997; Banno et al. 2012).