Leflunomide--an immunomodulator--induces regression of endometrial explants in a rat model of endometriosis.

Objective: To test if leflunomide, an immunomodulator, could impede the growth of an ectopic uterine tissue.

Methods: Endometriosis was surgically induced in 26 rats by transplanting an autologous fragment of endometrial tissue onto the inner surface of the abdominal wall. Four weeks later two rats were killed. The volume and weight of the implants were measured. The remaining rats were randomly grouped, and in group 1 no medication was given. To the rats in group 2, 35 mg/kg/d of leflunomide was administered orally. Four weeks later, rats were killed and ectopic uterine tissues were reevaluated morphologically and histologically. A scoring system was used to evaluate preservation of epithelia.

Results: Two rats in the control group died 5 weeks after surgery. There was a significant difference in post-treatment spherical volumes (139.1 +/- 92.8 versus 33.5 +/- 12.5 mm3) and explant weights (156.3 +/- 105.6 versus 38.6 +/- 12.6 mg) between the control and leflunomide-treated groups. The epithelia were found to be preserved significantly better in the control group when compared with the leflunomide-treated group (median 2.5 [interquartile range, 1.25] versus median 1.00 [interquartile range, 1.5]).

Conclusion: Leflunomide appeared to cause regression of experimental endometriosis in rats.