Immunohistochemistry using
monoclonal antibodies against human
inhibin, a peptide hormone produced by ovarian granulosa cells to inhibit
follicle-stimulating hormone (FSH), has been recently applied to diagnostic anatomic pathology. This investigation hypothesizes that
inhibin immunohistochemistry will aid in the crucial clinical distinction between sex cord-stromal and other primary
ovarian neoplasms. Available H&E slides and clinical information from a retrospective surgical series of 186 primary ovarian
tumors were reviewed to verify diagnoses, and representative
paraffin sections were immunostained with anti-
inhibin (R1 monoclonal, Serotec, Kidlington, Oxford, UK). Immunoreactivity was graded as weak/strong (W/S), and the proportion of strong staining cells was coded as follows: S1 = <10%, S2 = 10%-50%, S3 = >50%, respectively.
Inhibin immunoreactivity for 137 sex cord-stromal lesions was as follows: 100% of 66
granulosa cell tumors: 80% S3, 20% S2; 100% of 17 Sertoli-stromal
tumors: 90% S3, 10% S2; 100% of 13 hyperplastic follicular/stromal lesions: 90% S3, 10% S2; 100% of six
steroid cell
tumors: 100% S3; 90% of 18
thecomas: 40% S3, 10% S2, 10% S1, 30% W; 0% of 12
fibromas, three
myxomas, and two sclerosing stromal
tumors. None (0 of 49) of the other
ovarian neoplasms exhibited
inhibin: 22
carcinomas, 12
carcinosarcomas, seven
small cell carcinomas, six
germ cell tumors, and two
lymphomas. In the typical case, the distinction between sex cord-stromal and other
ovarian neoplasms requires nothing more than routine pathological examination. In diagnostically challenging cases, our data indicate that
inhibin immunohistochemistry is a very useful adjunct because granulosa and sertoli-stromal
tumors are positive whereas other potential mimickers have been negative thus far.