Pax8: a marker for carcinoma of Müllerian origin in serous effusions.

TLDR: Examination of PAX8 expression in the normal uterine corpus and cervix, malignant tumors arising from these sites, and malignant effusions suggests that PAX8 is an additional IHC marker for carcinomas of Müllerian origin, and recommends including PAX8 for evaluation of malignant serous effusions in women.

Abstract: PAX8 is a nuclear transcription factor with limited expression in normal and neoplastic tissues in a cell lineage-dependent manner. PAX8 has been detected in embryonic Mullerian ducts, human fallopian tubes, and ovarian carcinomas. However, little is known about its expression in other areas of the female genital tract. In this study, we used immunohistochemistry (IHC) to examine PAX8 expression in the normal uterine corpus and cervix, malignant tumors arising from these sites, and malignant effusions. We reported here that PAX8 was also detected in endometrial epithelial cells and endocervical glands, with a lower expression level in the latter, but not in the stromal cells of these areas. All endometrial carcinomas (N = 52) were positive for PAX8, whereas endocervical adenocarcinomas (N = 5) and uterine leiomyosarcomas (N = 3) were negative for PAX8. PAX8 was detected in 70% (22/31) and 68.8% (11/16) of metastatic carcinomas of the ovary and endometrium in serous effusions, respectively. No PAX8 was detected in carcinomas of nongynecologic origin or noncarcinomas (N = 71) in serous effusions except in one renal-cell carcinoma and one carcinoma of unknown primary in a woman. In addition, papillary serous carcinomas of the peritoneum (N = 10) were diffusely positive for PAX8, implying a Mullerian origin similar to malignant tumors in the female genital tract. Our findings suggest that PAX8 is an additional IHC marker for carcinomas of Mullerian origin hence we recommend including PAX8 for evaluation of malignant serous effusions in women, especially when tumors of Mullerian origin are in the differential diagnosis.