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

Objective: To examine endometrial response to long-term low-does RU486 administration.

Design: Retrospective controlled study of women with endometriosis treated for 6 months with 50 mg RU486 daily for 6 months. Controls consisted of women in the follicular phase of a spontaneous cycle undergoing endometrial biopsy.

Setting: Patients from the clinical practice of the authors at the University of California, San Diego Medical Center.

Patients And Interventions: Nine patients treated with long-term low-dose RU486 and nine normal cycling controls undergoing hysterectomy or endometrial biopsy for benign disease.

Main Outcome Measures: Changes in endometrial morphology and immunohistochemical analysis for estrogen receptor (ER) and progesterone receptor (PR) protein.

Results: All patients treated with RU486 exhibited abnormal endometrial morphology. The endometrial glands were irregular in size and shape. The stroma was varied but consisted predominantly of dense cellular stroma with frequent mitotic figures. The glands were lined by a combination of epithelial types some of which were secretory. No cytologic atypia was seen. Levels of ER immunoreactivity, as determined by image analysis, were greater in the stroma with no difference in PR immunoreactivity compared with controls. No difference in ER and PR immunoreactivity were seen in the glands compared with normal controls.

Conclusion: The generalized cystic changes demonstrated are consistent with a chronic unopposed estrogen effect and are concordant with hormonal data showing early to midfollicular phase levels of estrogens. They also are consistent with our findings of increased ER immunoreactivity in the stroma. Evidence of minimal P agonist effect was noted.