SF-1 is a diagnostically useful immunohistochemical marker and comparable to other sex cord-stromal tumor markers for the differential diagnosis of ovarian sertoli cell tumor

Immunohistochemistry can be an important part of the diagnosis of Sertoli cell tumor of the ovary, including distinction from non-sex cord-stromal tumors such as the sertoliform variant of endometrioid carcinoma and carcinoid. Several good markers for this differential diagnosis have been identified, particularly inhibin, Wilms tumor 1 gene product (WT1), epithelial membrane antigen, and chromogranin; however, many available markers have limitations to some degree. Steroidogenic factor 1 (SF-1; adrenal 4-binding protein; Ad4BP) is a nuclear transcription factor involved in gonadal and adrenal development. In the testes, SF-1 is expressed in Sertoli cells. Immunohistochemical expression of this marker in ovarian sex cord-stromal tumors, including utility for differential diagnosis, has not been rigorously evaluated. As an extension of our previous immunohistochemical studies of ovarian Sertoli cell tumor, expression of SF-1 and comparison with WT1 and inhibin were assessed in 111 primary ovarian tumors: 27 Sertoli cell tumors, 60 endometrioid tumors (including borderline tumors, conventional well-differentiated carcinomas, and sertoliform variants of carcinoma), and 24 carcinoids. SF-1 was expressed in 100% of Sertoli cell tumors but not in endometrioid tumors or carcinoid. WT1 was expressed in 100% of Sertoli cell tumors and 17% of endometrioid tumors; all carcinoids were negative. Inhibin was expressed in 96% of Sertoli cell tumors and 2% of endometrioid tumors (4% of conventional well-differentiated carcinomas); all carcinoids were negative. The extent of expression of all 3 markers was similar in Sertoli cell tumor but greatest for WT1: 63%, 96%, and 78% of cases showed expression of SF-1, WT1, and inhibin, respectively, in more than 50% of tumor cells. Immunohistochemical composite scores combining both extent and intensity of staining in positive cases were calculated for Sertoli cell tumor (possible range: 1-12). Combined extent/intensity of immunostaining was similar for all 3 markers, but WT1 showed the most robust immunoreactivity in positive cases (mean immunohistochemical composite scores for SF-1, WT1, and inhibin: 6.1, 10.8, and 7.8, respectively). We conclude that for the differential diagnosis with endometrioid tumors and carcinoid of the ovary, SF-1 is a sensitive and specific immunohistochemical marker for Sertoli cell tumor and that SF-1 is diagnostically comparable with other good sex cord-stromal markers.