Estrogen receptor localization in formalin-fixed, paraffin-embedded endometrium and endometriotic tissues

Monoclonal estrogen receptor (ER) antibody and indirect immunoperoxidase techniques were used to study the immunohistochemical localization of ER in paraffin sections of 20 surgical specimens containing foci of endometriosis. The eutopic endometrium, available in 16 of 20 cases, was dated histologically and stained for ER. Specific nuclear staining was observed in glandular and stromal cells of the endometrium during the proliferative and early secretory phases. Mid and late secretory phase endometria showed only focal staining. Dating of the endometriotic tissues using morphologic criteria revealed that these were in phase with the endometrium in nine of 16 cases. In these cases the ER staining of both the endometriotic tissues and endometrium was similar. The endometriotic tissues could not be dated as either proliferative or secretory in seven cases and stained variably for ER. Diffuse nuclear staining for ER was present in the endometriotic glands of three of these cases in which the endometriotic glands morphologically resembled glands of the basalis contrasting with weak, focal staining in the corresponding eutopic secretory endometria. The majority of endometriotic tissues examined mimicked the cyclic ER expression of the eutopic endometrium and thus appeared to correspond to the morphologic appearance of the endometriotic glands. Immunohistochemical staining with monoclonal estrophilin antibodies may be helpful in supporting the histopathologic diagnosis of endometriosis.