Pleuro-pulmonary endometriosis in baboons (Papio spp.): insights into pathogenesis

Background Human pleuro‐pulmonary endometriosis (PPE) is rare. Recently, we identified several cases of abdominal endometriosis in baboons that developed PPE. Materials and Methods Ten cases of PPE and four of intra‐abdominal endometriosis (three simultaneous) were identified at necropsy in baboons (Papio spp.) found dead due to natural causes. The endometriotic lesions were evaluated using immunohistochemistry. Results The stromal (CD10+) and epithelial cells in intra‐abdominal cases were estrogen and progesterone receptor (ER/PR) positive and thyroid transcription factor 1 (TTF‐1) negative similar to that seen in humans. In contrast, the PPE cases displayed TTF‐1‐positive epithelium lining the cystic spaces, while the stroma was ER/PR positive similar to that in abdominal endometriosis. Both lymph nodes and spindle cell rests in lung interstitium contained ER/PR‐positive stromal cells. Conclusions The lung lesions were different from the abdominal lesions in having a TTF‐1‐positive lining epithelium. The deep pulmonary interstitial and lymph node endometrial stromal rests probably arrive via lymphatic route. The endometrial stroma is the driving force in PPE upon which the lung‐specific epithelium condenses and may require a novel approach to therapy.