IMMUNOHISTOCHEMICAL ANALYSIS OF THE PERITONEUM ADJACENT TO ENDOMETRIOTIC LESIONS USING ANTIBODIES FOR BER-EP4 ANTIGEN, ESTROGEN-RECEPTORS, AND PROGESTERONE RECEPTORS - IMPLICATION OF PERITONEAL METAPLASIA IN THE PATHOGENESIS OF ENDOMETRIOSIS

This study was designed to investigate whether or not the pelvic perit oneum exhibits a metaplastic process into mullerian-type epithelium us ing a marker for epithelial differentiation (Ber-EP4 antigen) and mark ers that indicate mullerian differentiation (estrogen receptors and pr ogesterone receptors). The peritoneum and/or ovarian surface epitheliu m adjacent to endometriotic lesions were obtained from 24 patients wit h endometriosis at operation, and peritoneum and ovarian surface epith elium without any lesions were also obtained from control patients wit hout endometriosis. The specimens were immunohistochemically analyzed using antibodies for epithelial antigen Ber-EP4, estrogen receptor (ER ), and progesterone receptor (PR) on frozen sections. Normal peritonea l mesothelium showed negative staining for Ber-EP4, ER, and PR. The me sothelium of the peritoneum adjacent to the endometriotic lesions show ed focal positivity for Ber-EP4, ER, and PR. Several cases of ovarian surface epithelium from normal control ovaries and ovaries adjacent to endometriotic lesions also showed focal positivity for Ber-EP4, ER, a nd PR. Stromal cells accompanying these foci were sporadically positiv e for ER and/ or PR but negative for Ber-EP4. Focal expression of Ber- EP4, ER, and PR in the mesothelium of the peritoneum and the ovarian s urface epithelium adjacent to endometriotic lesions suggests that meso thelium possibly acquires characteristics of epithelial as well as mul lerian-type nature. These results support an existence of a metaplasti c process of the peritoneal mesothelium in the pathogenesis of endomet riosis. The more frequent Ber-EP4 positivity in normal ovarian surface epithelium compared to normal peritoneal mesothelium also suggests a fundamental difference in these tissues that may be related to the gre ater prevalence of epithelial neoplasms arising in ovarian tissue.