Ovarian
sex cord-stromal tumors are a morphologically diverse group of
neoplasms that can mimic the appearance of other ovarian
tumors. Because the treatment and prognosis of
sex cord-stromal tumors differs substantially from those of other
ovarian neoplasms, the development of an immunohistochemical panel to support the diagnosis of the former group of
tumors would be useful. In this report, the utility of immunostaining for
inhibin alpha,
epithelial membrane antigen, MIC2 gene
protein product, and
keratin in the differential diagnosis of
sex cord-stromal tumors was assessed in
formalin-fixed,
paraffin-embedded sections. In addition, the immunohistochemical staining pattern of ovarian
small cell carcinomas (SCCs), hypercalcemic type, was analyzed in an attempt to clarify the histogenesis of these
tumors. Thirty-two (97%) of 33
granulosa cell tumors (GCTs), 10 (91%) of 11
Sertoli-Leydig cell tumors (SLCTs), and 4 (8%) of 51
carcinomas showed
inhibin alpha immunopositivity. None of the 3
lymphomas, 5
carcinoids, 6
dysgerminomas, or 12 SCCs showed
inhibin alpha positivity. Eighteen (55%) GCTs, 6 (55%) SLCTs, 6 (12%)
carcinomas, and 7 (58%) SCCs showed MIC2 gene expression. None of the GCTs and only one SLCT showed
epithelial membrane antigen (EMA) positivity, although 92% of surface epithelial
carcinomas and 75% of SCCs were immunoreactive. These data suggest that detection of
inhibin immunoreactivity in an ovarian
tumor that is EMA-negative provides both sensitive and specific support for the diagnosis of a
sex cord-stromal tumor. Because SCCs generally
stain for EMA but not for
inhibin, it appears that SCCs probably represent a variant of surface epithelial
tumor rather than a type of
sex cord-stromal tumor.