The diagnostic utility of inhibin staining in ovarian neoplasms

Previous immunohistologic studies have suggested that the antibody to the alpha subunit of inhibin is a sensitive marker of sex cord-stromal differentiation. However, detection has also been reported within both ovarian epithelial and germ cell tumors. To further study the normal tissue distribution of inhibin and the utility of its detection for the differential diagnosis of ovarian sex cord-stromal neoplasms, normal tissues and 225 lesions including sex cord-stromal lesions, ovarian epithelial and stromal cancers, ovarian and testicular germ cell tumors, metastases to the ovary, and non-ovarian cancers were analyzed using semi-automated immunohistochemistry. In normal tissues, immunostaining was found in cell subsets of the ovary, testis, adrenal gland, placenta, and kidney. All sex cord-stromal tumors were inhibin-positive and 37 of 50 (74%) cases exhibited at least moderate to strong immunostaining. Two cases originally diagnosed as adult granulosa cell tumors that were inhibin-negative were reassessed; diagnoses of endometrioid stromal sarcoma and endometrioid carcinoma with sertoliform features were rendered. In other primary or metastatic ovarian lesions or metastases to the ovary, weak to moderate immunostaining was found in only 4 of 84 (4.8%) cases, including ovarian clear cell carcinoma (2/2), uterine clear cell carcinomas metastatic to the ovary (1/3), and serous papillary carcinoma (1/2). Similarly, only 4 of 66 (6.1%) non-ovarian neoplasms exhibited weak immunostaining, including melanoma (1/5), uterine endometrioid carcinoma (1/2), transitional cell carcinoma (1/3), and breast adenocarcinoma (1/8). Only one case of a non-sex cord-stromal tumor had moderate or strong immunostaining. Based on these results, immunohistologic detection of the alpha subunit of inhibin is a useful adjunct in the differential diagnosis of sex cord-stromal neoplasms.