Endometriosis: Immunohistochemical analysis of oestrogen and progesterone receptors in endometriotic tissue and endometrium

The objective of the study was to compare the localization and staining intensity of oestrogen and progesterone receptors in endometrium and endometriotic tissue. Using monoclonal antibodies towards oestrogen and progesterone receptors, analysis was performed in 63 endometriotic samples from 40 women and compared to endometrium obtained simultaneously from 25 of the women. Using a staining index, ‘total immuno-staining score’, calculated from the staining intensity multiplied by the fraction of positive cells, the receptor content was estimated semiquantitatively. The scores for both oestrogen and progesterone receptors were lower in endometriotic epithelial cells than in endometrial epithelial cells, but the differences reached statistical significance only for the progesterone receptor. No difference was found for stromal cells. There was a significant correlation between oestrogen receptor score in endometriotic tissue and in endometrium, but not for progesterone receptor score. In endometrium and vaginal and peritoneal endometriosis, the progesterone receptor score showed similar values, higher than those in ovarian endometriosis. The data from this large immuno-histochemical study support previous results of quantitative steroid receptor analyses, indicating that the regulation of steroid effects, especially those of progesterone, differs between endometriotic and endometrial tissue.