Monoclonal antibodies against inhibin represent key markers of adult granulosa cell tumors of the ovary even in their metastases. A report of three cases with late metastasis, being previously misinterpreted as hemangiopericytoma.

Antibodies against human inhibin, a peptide hormone produced by ovarian granulosa cells to inhibit FSH, are widely applied to determine serum inhibin levels. Recently, they were, however, proved also to stain follicle cells in ovarian tissue by immunoreactions in histological sections. The commercially available inhibin antibody produced by Serotec, applied to sections of paraffin blocks, stained follicle epithelia in 6/6 samples of ovarian tissue from females under the age of 40 recruited from the archives. Adult granulosa cell tumor tissue samples from primary tumors of the ovary showed positive reaction in 6/6 cases. No positive reaction was found in staining tissues from hemangiopericytomas from males (0/3), leiomyomas, leiomyosarcomas, and a malignant melanoma (0/5), serving as negative controls. No positive reactions could be observed in tumor cells of 10 ovarian carcinomas, whereas in two of these cases single cells of the specialized ovarian stroma stained positively with inhibin. Positive immunostainings were revealed in three late metastases (two within the liver) from granulosa cell tumors in females, primarily misinterpreted as hemangiopericytomas or leiomyosarcomas, because the previously resected primaries of the ovary were not known at the time of liver surgery. The recognition of granulosa cell tumors, especially the distinction of the sarcomatoid growth type from soft tissue tumors, may be difficult, even if immunostaining for intermediate filaments are applied. Immunostaining by antibodies against inhibin, which can be applied reliably in histopathology, may therefore provide a useful tool to distinguish between granulosa cell tumors and genuine soft tissue tumors. This is also of clinical importance, because treatment of the former by cisplatin-based polychemotherapy and antisex hormone therapy proved to be helpful. Furthermore, the inhibin antibody can be used as an early serum marker for detecting tumor recurrence months before clinical evidence.