IFITM1 is a Novel, Highly Sensitive Marker for Endometriotic Stromal Cells in Ovarian and Extragenital Endometriosis.

When the presence of endometriotic lesions are not evident by hematoxylin and eosin staining, CD10 is used to highlight and confirm the presence of endometriotic stroma. However, CD10 is not specific only to the endometrial stroma but is also expressed in many other cells. Recently, interferon-inducible transmembrane protein 1 (IFITM1) was reported as a highly specific immunohistochemical marker of normal endometrial stroma and endometrial stromal neoplasm. In this study, we examined the expression of IFITM1 and CD10 in 18 cases of ovarian endometriosis and 44 cases of extragenital endometriosis. Among the 62 patients, 62 (100.0%) were positive for IFITM1 and 60 (96.8%) for CD10, and CD10 was negative in 2 cases that were positive for IFITM1. Additionally, we found that IFITM1 sensitivity was unaffected by the presence or absence of hormonal therapy. To the best of our knowledge, this represents the first demonstration of IFITM1 as a highly sensitive stromal marker of ovarian and extragenital endometriosis.