Estrogen and progestin receptors in endometriosis lesions: comparison with endometrial tissue.

Cytosol estrogen (ER) and progestin (PR) receptors were quantified in 47 endometriosis lesions from 41 patients and compared with receptor measurements in the endometrial tissue of nine of these patients. Half of the specimens of endometriosis tissue contained PR only, in concentrations that were significantly lower than in the endometrium. Only 30% of the specimens of endometriosis tissue contained the two receptors simultaneously, and levels of ER were very low compared with those in the endometrium. Levels of PR in the specimens of endometriosis tissue were highest at the periovulatory period, whereas concentrations of ER tended to be highest at the beginning and close to the end of the cycle. These results suggest that regulation of these receptors is dissimilar in endometriosis lesions and endometrium. It remains to be seen whether differences in receptor distribution in the lesions of individual patients could explain differences in the course of this disease, and have therapeutic implications. The presence of PR in the majority of the endometriosis lesions is in accord with the favorable therapeutic response often obtained with progestin treatment of this disease.