Endometriosis is the growth of endometrial lesions outside of the uterus – these lesions are adherent on various organs in the peritoneum, including the ovaries. It is a major painful and debilitating disease of women of reproductive age. It is also a major cause of infertility and involves both inflammatory pain and tissue proliferation. Past and current endocrine therapies for the treatment of endometriosis have generally proven ineffective. In cases where they have been able to cause reduction in lesions, they have not been very effective in reducing pain. Dr. John Katzenellenbogen and colleagues have developed novel compounds targeting estrogen receptor β (ERβ), one of the two ERs found in uterine tissue and endometrial lesions. These compounds possess growth-suppressive and anti-inflammatory activities. In studies in established mouse models of endometriosis, the compounds prevented the formation of endometriotic lesions and significantly reduced previously established lesions. Immune cell infiltration and markers of inflammation were also suppressed. Formation of new blood vessels and development of nerve patterns following these vessels (likely targeting pain symptoms) were also suppressed in the animal studies.