IMMUNOHISTOCHEMICAL EXPRESSION OF INHIBIN/ACTIVIN SUBUNITS IN EPITHELIAL AND GRANULOSA CELL TUMOURS OF THE OVARY

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Abstract
Dimeric inhibin‐A has been shown recently by a sensitive two‐site ELISA assay to be a useful tumour marker in granulosa cell tumours of the ovary. It is also elevated in some patients with malignant epithelial ovarian tumours. To identify the precise subunits of inhibin expressed in ovarian tumours, three monoclonal antibodies, R1, E4, and INPRO (against the αC‐, βA‐, and pro‐α‐subunits, respectively), were evaluated by immunohistochemistry on a panel of six granulosa cell and nine epithelial tumours. All granulosa cell tumours stained positively with E4 and R1, suggesting expression of dimeric inhibin‐A; in two patients where serum levels were measured pre‐operatively, they were elevated. The tumours also reacted weakly with INPRO, suggesting the presence of precursor forms of the α‐subunit. Eight malignant epithelial ovarian tumours expressed the βA‐subunit only, as recognized by E4, while one tumour expressed both α‐ and βA‐subunits, which correlated with an elevated serum inhibin‐A level. Thus, while granulosa cell tumours express inhibin, the majority of epithelial tumours probably express activin, a result which needs to be confirmed by serum measurements. © 1997 by John Wiley & Sons, Ltd.