Diagnostic utility of PAX8 in differentiation of mullerian from non-mullerian tumors

Considering the high prevalence of female genital tract neoplasms, non-specific nature of the initial symptoms, higher possibility of metastasis by the time of diagnosis, importance of differentiating metastatic Mullerian tumors or metastatic breast cancer in the female genital tract, especially in the ovary, and lack of diagnostic markers with high sensitivity and specificity, the purpose of the current study was to evaluate the utility of Paired box protein8 (PAX8) expression in Mullerian and non-Mullerian neoplasms.

In this descriptive–analytic, cross-sectional study, paraffin-embedded tissues of patients with definitive pathologic diagnosis of Mullerian and non-Mullerian tumors were selected. PAX8 immunohistochemical (IHC) staining was performed for all selected blocks. Immunopositivity of the slides for PAX8 was reviewed. It was defined as the presence of nuclear staining in at least 10% of the tumor cell nuclei.

Thirty-seven Mullerian (including 18 ovarian epithelial tumors, 17 endometrial carcinoma and two endocervical adenocarcinoma) and 37 non-Mullerian tumors were studied for PAX8 expression. Twentynine of 37 (78.4%) and one of 37 (2.7%) of the Mullerian and non-Mullerian tumors were positive for PAX8, respectively. The sensitivity and specificity of PAX8 by IHC for differentiation of Mullerian from non-Mullerian tumors was 78.4% and 97.3%, respectively.

Our findings indicated that PAX8 could be used as a useful IHC marker for diagnosing Mullerian tumors. It has moderate to high sensitivity, but high specificity, for diagnosing carcinomas of Mullerian origin.