Endometrial effects of long-term low-dose administration of RU486

Area of Science:

• Reproductive Endocrinology
• Gynecologic Pathology

Background:

• Endometriosis is a common gynecologic condition.
• Hormonal therapies are used to manage endometriosis symptoms.

Purpose of the Study:

• To evaluate the endometrial response to long-term, low-dose mifepristone (RU486) administration in women with endometriosis.

Main Methods:

• Retrospective controlled study involving nine women with endometriosis treated with 50 mg RU486 daily for six months.
• Endometrial morphology and immunohistochemical analysis for estrogen receptor (ER) and progesterone receptor (PR) were assessed.
• Controls included nine women in the follicular phase of a spontaneous cycle.

Main Results:

• RU486-treated patients showed abnormal endometrial morphology, including irregular glands and dense, cellular stroma with mitotic figures.
• Increased ER immunoreactivity was observed in the endometrial stroma compared to controls.
• No significant difference in PR immunoreactivity was found in the stroma or glands between groups.

Conclusions:

• The observed endometrial changes suggest a chronic unopposed estrogen effect, consistent with early to mid-follicular phase estrogen levels.
• Increased stromal ER immunoreactivity supports the hypothesis of unopposed estrogen action.
• Minimal progesterone agonist effect was noted, indicating incomplete blockade by RU486.