Proliferative activity of postmenopausal endometriosis: a histopathologic and immunocytochemical study.

Histological features of 21 cases of postmenopausal endometriosis as well as the corresponding eutopic endometrium were studied. Immunocytochemical analysis of estrogen receptor (ER), progesterone receptor (PR), and Ki-67 nuclear antigen was also performed on the endometriotic lesions as well as the corresponding endometrium. All the cases studied were complicated by various other gynecologic diseases, making the preoperative diagnosis of endometriosis unlikely. Histologically, the endometriotic foci contained both epithelial and stromal components mostly lacking atrophic features in contrast to the corresponding eutopic endometrium. The endometriotic lesions and the corresponding endometrium exhibited immunoreactivity with ER in both the glands and stroma. The stromal cells of endometriotic lesions revealed positive PR staining, whereas those of the eutopic endometrium were either negative or weakly positive for PR, but the epithelial components of both were positive for PR. The positivity of Ki-67 antigen tended to be higher in the stroma of the postmenopausal endometriosis than in the eutopic endometrial stroma. Endometriotic lesions appear to remain biologically active, with proliferative activity as well as retained hormonal responsiveness, even in the low-estrogen milieu of the postmenopausal age.