Value of A103 (melan-A) immunostaining in the differential diagnosis of ovarian sex cord stromal tumours.

AIMS To assess A103 (melan-A) immunoreactivity in a range of ovarian sex cord stromal tumours and to evaluate it for the differential diagnosis of other neoplasms. METHODS Paraffin embedded tissue sections from 45 sex cord stromal tumours and 44 potential histological mimics were examined immunohistochemically using the antibody A103. The sex cord stromal group included 21 adult granulosa cell tumours (AGCT), two juvenile granulosa cell tumours (JGCT), eight tumours showing Sertoli cell or Sertoli-Leydig cell differentiation, two unclassified tumours, two gonadoblastomas, one sex cord tumour with annular tubules, two steroid cell tumours, five thecomas/fibrothecomas, and two sclerosing stromal tumours. The histological mimics include 14 primary ovarian carcinomas, 13 metastatic carcinomas, four carcinoid tumours, four lymphomas, three endometrioid stromal sarcomas, two ovarian tumours of probable Wolffian origin, and one case each of small cell carcinoma, desmoplastic small round cell tumour, melanoma, and primitive neuroectodermal tumour. RESULTS A103 immunoreactivity was identified in 25 sex cord stromal tumours including 10 AGCT, two JGCT, six Sertoli/Sertoli-Leydig cell tumours, two steroid cell tumours, three thecomas/fibrothecomas, and two sclerosing stromal tumours. Of the potential histological mimics, staining was present only in the two ovarian tumours of probable Wolffian origin and the melanoma. Immunoreactive stromal cells were noted in a minority of cases. Normal hilus cells and rete ovarii epithelium also expressed A103. CONCLUSIONS A103 is a moderately sensitive and specific marker of sex cord stromal differentiation within the range of tumours examined in this study and as such is a valuable adjunct to other immunocytochemical markers in the assessment of diagnostically problematic ovarian tumours. The staining of normal and neoplastic Wolffian elements merits further investigation.