This study investigated the immunohistochemical expression and localization of neutral endopeptidase (NEP) (CD10), which plays a functional role by degrading bioactive peptides, in ovarian tumors. In normal ovaries and benign cystadenomas, NEP was not detected in any epithelial or stromal cells. In borderline tumors, NEP was detected in the stromal cells in 6 of 7 serous tumors, but not in those from mucinous tumors. In ovarian carcinomas, NEP in the stromal cells was observed in 13 of 20 serous, 8 of 10 endometrioid, and 7 of 10 clear-cell adenocarcinomas. NEP was weakly detected in only 1 of 9 mucinous adenocarcinomas. The staining intensity of stromal NEP was decreased in grades 2 and 3 serous carcinomas compared with that in grade 1 serous carcinomas. In conclusion, NEP was specifically expressed in the stroma of borderline and malignant ovarian tumors, but not in adenomas. Furthermore, stromal NEP was downregulated as the histological grade advanced. These results suggest that NEP may play a role in the regulation of neoplastic transformation and tumor differentiation in epithelial ovarian carcinomas.
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