Inhibin Forms in Serum From Postmenopausal Women With Ovarian Cancers

There are reports that serum inhibin, a glycoprotein produced by the gonads that inhibits pituitary FSH secretion, is increased in postmenopausal women having mucinous or granulosa cell cancer of the ovary. Because a radioimmunoassay (RIA) directed to the α subunit of inhibin is more often elevated than an inhibin A enzyme-linked immunoassay (ELISA), it may be that these cancers produce inhibin B or the free α subunit. This study attempted to identify different forms of inhibin in 143 postmenopausal women with ovarian cancer and 23 others with other cancers. Eleven of the former women had granulosa cell tumors. Sera were also obtained from 34 healthy postmenopausal women and 8 postmenopausal women who had undergone bilateral salpingo-oophorectomy for reasons other than malignant disease. The results of ELISAs for inhibin B and the Pro-αC subunit were compared with those of an inhibin A ELISA and an inhibin RIA.All of the granulosa cell tumors were detected by the inhibin RIA and the ELISA for inhibin B; 90 percent were detected by the Pro-αC ELISA; and 77 percent were detected by the inhibin A ELISA. Of 20 mucinous cystadenocarcinomas, 70 percent were detected by RIA, 60 percent by the inhibin B ELISA, 55 percent by the Pro-αC ELISA, and only 20 percent by the inhibin A assay. The 66 serous cystadenocarcinomas were detected 41 percent of the time by RIA but in fewer than 30 percent of cases using other assays. Serum FSH levels correlated inversely with inhibin A and inhibin RIA results in patients with granulosa cell cancer but not in patients having mucinous or other types of ovarian cancer. It seems that ovarian cancers can produce a range of inhibin-related peptides, including dimeric inhibins A and B. Assays that detect all forms of inhibin incorporating the α subunit probably will detect more of these cancers than those identifying the Pro-αC subunit. Inhibin estimates are a useful marker of ovarian disease only in postmenopausal women, whose serum inhibin levels are relatively low. It may, however, prove helpful to measure inhibin after surgery for ovarian cancer even in premenopausal women if they possess cancer-specific forms of inhibin.