Immunohistochemical findings. a) Cytokeratin 7 positivity limited to endometriotic epithelium. b) Cytokeratin 20 positivity limited to intestinal-type epithelium. c) CD10 positivity of endometriotic stroma on which both endometriotic and intestinal-type epithelilia rest. d) CD10 positive endometriotic stroma surrounding intestinal-type glands. (e and f) ER positivity of endometriotic epithelium and stroma, but absence in metaplastic epithelium. g) Rare ER positive “transitional” cells with intestinal-type differentiation (arrows).