Inhibin Forms in Serum From Postmenopausal Women With Ovarian Cancers

Abstract

BACKGROUND AND OBJECTIVE Previous studies have shown that serum inhibin as measured by α subunit-directed radioimmunoassay (RIA) and inhibin A ELISA was elevated in postmenopausal women with mucinous and granulosa cell cancers, with the RIA showing a more frequent elevation than the inhibin A ELISA. It was thus hypothesised that these cancers may also produce inhibin B or the free α subunit. The aim of the study was to identify the forms of inhibin found in a range of ovarian cancers using a range of inhibin assays with varying specificities. DESIGN Serum samples obtained from women with ovarian cancer were assayed by inhibin B ELISA and Pro-αC subunit ELISA and compared with inhibin RIA and inhibin A ELISA. PATIENTS Blood samples were obtained from 34 postmenopausal women (>55 years) with no history of endocrine disease and from women with ovarian serous cystadenocarcinomas (n = 66), mucinous cystadenocarcinomas (n = 20), granulosa cell tumours (n = 9 − 11), miscellaneous ovarian cancers (n = 46) and non ovarian cancers (n = 23). MEASUREMENTS Inhibin B and inhibin Pro-αC subunit levels were determined by ELISA and compared to values obtained by RIA and inhibin A ELISA. Cancers were discriminated from controls based on values obtained 2SD above the geometric mean of the control values. RESULTS Granulosa cell tumours were detected by RIA and inhibin B ELISA (100%), Pro-αC ELISA (90%) and inhibin A ELISA (77%). Mucinous tumours were detected by RIA (70%), inhibin B ELISA (60%), Pro-αC ELISA (55%) and inhibin A (20%). Serous tumours were detected by RIA (35%) and the other assays (<15%). Miscellaneous tumours were detected by RIA (41%) and other assays <30%. CONCLUSIONS Ovarian neoplasms may produce a variety of peptides related to the inhibins, including dimeric inhibin A and B. Inhibin B is detected in more ovarian cancers than inhibin A but does not discriminate as well as the α subunit directed assays. The higher discrimination index obtained with the RIA compared to the Pro-αC ELISA suggests that assays detecting all inhibin forms containing the α subunit and not just those detecting the Pro-αC subunit will provide the most useful detection method.