Inhibin and activin: Their roles in ovarian tumorigenesis and their diagnostic utility in surgical pathology practice

Bioactive inhibins (alpha plus beta subunit) and activins (two beta subunit s) are related nonsteroidal dimeric proteins by virtue of their sharing two common beta subunits. initially, both inhibin and activin were believed to act exclusively as endocrine nonsteroid hormones. It soon became apparent that inhibin and activin subunits were expressed in a wide variety of gonad al and nongonadal tissues, suggesting that these peptides have other functi ons in addition to regulating follicle-stimulating hormone (FSH) secretion. Recently, inhibin alpha has been proposed to be a sex cord-stromal differe ntiation marker, and much interest has arisen regarding the roles of inhibi n and activin in the pathogenesis and diagnosis of both ovarian epithelial and sex cord-stromal tumors (SCSTs), In this article, we briefly review the structure of bioactive inhibin and activin and their tissue distribution. We present the current opinion regarding the function of both inhibin and a ctivin in the development of ovarian tumors. The important progress in the field is summarized. Considerable interest in the topic of inhibin has grow n in the fields of surgical pathology and immunohistochemistry. After inhib in alpha was first reported as an immunohistochemical marker of granulosa c ell tumors in 1995, many reports regarding the use of inhibin alpha as a se nsitive diagnostic marker for gonadal SCSTs have been published. There is a need for a summary of current opinion for, among others, surgical patholog ists, both in training and in practice. In general, immunohistochemical sta ining of inhibin alpha proves to be a valuable diagnostic marker for ovaria n SCSTs, but caution should be paid in certain situations for the low speci ficity of inhibin tissue expression. The usefulness of inhibin alpha immuno staining in the diagnosis of ovarian SCSTs is summarized. The indications a nd limitations are also discussed.