Melan-A (A103) and inhibin expression in ovarian neoplasms

A103 is a melanocyte-associated monoclonal antibody that recognizes the Melan-A/MART-1 antigen in melanomas. The Melan-A/MART-1 antigen is also expressed in Leydig cells, adrenal tissue, and steroid-secreting tumors. A103 immunoreactivity in ovarian neoplasms, specifically sex cord stromal tumors (SCSTs), has not been well studied. Inhibin is known to be expressed in SCSTs but is also expressed in some carcinomas and other tumors. We sought to explore the usefulness of both antibodies in the diagnosis of ovarian neoplasms. Using conventional tissue sections and a tissue microarray, we studied the immunoreactivities of 131 ovarian tumors for A103 and inhibin: 30 SCSTs, including fibrothecoma, luteoma, hilus cell tumor, granulosa cell tumor, Sertoli-Leydig cell tumor, and sex cord tumor with annular tubules, and a control group of 96 surface epithelial tumors. A few other rare ovarian tumors including 1 small cell carcinoma, 1 adenocarcinoid tumor, 1 ovarian tumor of probable wolffian origin, 1 Krukenberg tumor, and 1 desmoplastic small round cell tumor were also studied. Inhibin staining was generally strong and diffuse in the majority of SCSTs (83%) and at least focally positive in the small cell carcinoma, ovarian tumor of probable wolffian origin, Krukenberg tumor, and desmoplastic small round cell tumor. Variable immunoreactivities were also present in 7 of 96 (7.3%) surface epithelial tumors. In comparison, A103 expression was usually weaker and more focal than that of inhibin and was present in a smaller proportion of SCSTs (37%) and negative in all the surface epithelial tumors. A103 was typically positive in the lipid-containing cells (both neoplastic and normal components) of these tumors (fibrothecomas, luteomas, Sertoli-Leydig cell tumors, hilus cell tumors, and granulosa cell tumors), and in some cases, moderate positivity was noted in these cells. Weak A103 positivity was identified in the single case of ovarian tumor of probable wolffian origin. A103 is relatively less sensitive than inhibin for recognizing SCSTs but does not appear to be expressed by ovarian surface epithelial tumors. It is therefore more specific than inhibin for SCSTs and is a useful marker for specifically identifying lipid-containing cells in tumors. Thus, adding A103 to a panel of markers including inhibin may be a valuable adjunct in the differential diagnoses of SCSTs and their distinction from other ovarian neoplasms.