Aromatase inhibitor treatment limits progression of peritoneal endometriosis in baboons

Suppression of aromatase cytochrome P450 may inhibit the in vivo growth of endometriosis lesions in baboons.

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David Langoi, D.V.M., Mary Ellen Pavone, M.D., Bilgin Gurates, M.D., Daniel Chai, D.V.M., Asgerally Fazleabas, Ph.D., Serdar E. Bulun, M.D.

Volume 99, Issue 3, Pages 656-662.e3, 1 March 2013



To determine the effect of inhibiting aromatase activity on endometrial lesion growth and aromatase expression in a baboon model of induced endometriosis.


Prospective study.


Institute of Primate Research, Nairobi, Kenya.


Sixteen olive baboons.


Sixteen olive baboons with induced endometriosis were examined with laparoscopy 10 months after disease inoculation . Animals in Group 1 (n=10) were treated with 1.25 mg/d of the aromatase inhibitor (AI) letrozole and animals in Group 2 (n=6) were given a placebo for a total of 6 months.

Main Outcome Measure:

Total number of endometriotic lesions, morphology and volume of leisions as well as semi-quantitative RT-PCR and quantitative PCR for levels of aromatase cytochrome mRNA were measured. Ovarian volumes were evaluated prior to treatment initiation and every 2 months during the study.


Treatment of Group 1 animals with an AI significantly decreased lesion volume from baseline measurements whereas the placebo-treated animals showed an increase in lesion volume . Aromatase mRNA levels in lesions in the AI-treated animals were significantly lower compared with the placebo-treated animals. Ovarian volumes were significantly increased at 6 months of AI treatment compared to pre-treatment volumes .


These findings suggest that suppression of aromatase cytochrome P450 may inhibit the in vivo growth of endometriotic lesions in baboons.

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Fertility and Sterility

Editorial Office, American Society for Reproductive Medicine

Fertility and Sterility® is an international journal for obstetricians, gynecologists, reproductive endocrinologists, urologists, basic scientists and others who treat and investigate problems of infertility and human reproductive disorders.