Hepatocytic differentiation in retiform Sertoli-Leydig cell tumors: distinguishing a heterologous element from Leydig cells.

Sertoli-Leydig cell tumors (SLCT) of the ovary are rare sex cord-stromal neoplasms. A minority of SLCT are characterized by a pattern resembling that of the rete ovarii and frequently have a range of homologous and heterologous tissues. Approximately 20 cases of SLCT have been reported to have elevation of serum alpha-fetoprotein (AFP) levels, or tissue immunoreactivity for AFP, a protein usually associated with germ cell neoplasms, especially yolk sac tumor. We identified hepatocytic differentiation in five cases of retiform SLCT (RSLCT), and confirmed immunohistochemically that these cells are hepatocytes rather than Leydig cells. Hepatocytes are positive for keratins (AE1/3 and Cam 5.2), AFP, and ferritin, negative for vimentin, and show weak to moderate staining for inhibin. Leydig cells are negative for keratins, positive for vimentin, and intensely positive for inhibin. Immunohistochemistry is needed to distinguish hepatocytic differentiation from Leydig cells with certainty. Including the cases in this report, hepatocytic differentiation has been associated with a retiform pattern in SLCT in 14 of 25 cases (56%). The association of these two patterns appears to be characteristic of a relatively primitive sex cord-stromal neoplasm.