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

Dimeric inhibin-A has been shown recently by a sensitive two-site ELIS A 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 (a gainst the alpha C-, beta A-, and pro-alpha-subunits, respectively), w ere evaluated by immunohistochemistry on a panel of six granulosa cell and nine epithelial tumours. All granulosa cell tumours stained posit ively with E4 and R1, suggesting expression of dimeric inhibin-A; in t wo patients where serum levels were measured pre-operatively, they wer e elevated. The tumours also reacted weakly with INPRO, suggesting the presence of precursor forms of the alpha-subunit. Eight malignant epi thelial ovarian tumours expressed the beta A-subunit only, as recogniz ed by E4, while one tumour expressed both alpha- and beta A-subunits, which correlated with an elevated serum inhibin-A level. Thus, while g ranulosa cell tumours express inhibin, the majority of epithelial tumo urs probably express activin, a result which needs to be confirmed by serum measurements. (C) 1997 by John Whey & Sons, Ltd.