IFITM1 Is Superior to CD10 as a Marker of Endometrial Stroma in the Evaluation of Myometrial Invasion by Endometrioid Adenocarcinoma.

Abstract

Background: Distinguishing myometrial invasion from adenomyosis involvement is important for staging of endometrial endometrioid adenocarcinoma. We aimed to compare CD10, which has limited value in this scenario, with interferon-induced transmembrane protein 1 (IFITM1), a recently described sensitive and specific marker of endometrial stroma. Methods: We reviewed 25 hysterectomies containing endometrial endometrioid adenocarcinoma and adenomyosis. Tumor areas were classified as unequivocally myoinvasive or unequivocally noninvasive. Foci equivocal for invasion were also recorded. Immunohistochemistry for IFITM1 and CD10 was performed and scored in terms of intensity and distribution and classified as negative or positive. Results: Unlike CD10, IFITM1 staining showed significant differences in mean intensity (P < .0001) and distribution (P < .0001) between invasive vs noninvasive areas. Sixteen (84.2%) invasive and 34 (97.1%) noninvasive areas were positive for CD10 (P = .22). In contrast, none of the invasive vs 25 (71.4%) noninvasive areas were positive for IFITM1 (P < .0001). IFITM1 had 71.4% sensitivity and 100% specificity in detecting stroma surrounding endometrioid adenocarcinoma, hence excluding myoinvasion. Eleven (45.8%) of 24 foci designated as equivocal stained with IFITM1. Conclusions: Compared with CD10, IFITM1 has superior performance distinguishing endometrial stroma of adenomyosis from mesenchyma surrounding invasive endometrial adenocarcinoma. IFITM1 expression is highly predictive of the absence of invasion and may be valuable in cases in which determining myoinvasion has staging implications.