Distinct clinicopathological features of ovarian endometriosis after long-term exposure to mifepristone

OBJECTIVE: Mifepristone has been used to treat endometriosis, but it can cause a constellation of endometrial alterations. Our study investigated the effects of long-term mifepristone on ovarian endometriosis. METHODS: We retrospectively analyzed the clinicopathological changes of ovarian endometriosis in 11 Chinese patients after long-term low-dose mifepristone therapy and compared these alterations with those observed in eutopic endometrium and adenomyosis side-by-side. Immunohistochemistry was applied to investigate estrogen receptor (ER), progesterone receptor (PR), and Ki67 expression in eutopic and ectopic endometrium. RESULTS: Nearly all patients had a pelvic mass and elevated serum CA125 levels. The ovarian lesions were grossly solid, cystic-solid, or cystic. They had a grayish–reddish appearance and a fleshy, honeycomb-like cut surface. The ovarian lesions shared morphological features with the uterine endometrium, and they were characterized by dilated, crowding endometrial glands with non-physiological changes. Immunostaining revealed consistent staining for ER and PR and a low Ki67 index in both eutopic and ectopic endometrium. CONCLUSIONS: Our findings suggest that ovarian endometriosis can mimic an endometrioid borderline tumor after long-term mifepristone administration. Careful histological assessment and related clinical information are critical for the correct interpretation of these rare entities.