Leydig cell tumor of the testis with histological and immunohistochemical features of malignancy in a 1-year-old boy with isosexual pseudoprecocity.

The article reports the clinical, histopathological, and immunohistochemical findings of a 1-year-old boy presenting with isosexual pseudoprecocity attributable to a functioning Leydig cell tumor of the testis. The case appears to represent the youngest patient ever recognized with this well-known syndrome. Malignancy features were also for the first time initially assessed using criteria, retrospectively developed from the literature, for metastasizing Leydig cell tumor. All the following were found: infiltrative borders, cellular pleomorphism, high mitotic index (12-14/high-power field), high MIB-1 index (40%), P53 positivity in 50% of the cells, and bcl-2 positivity in 15% of the cells. Immunohistochemistry proved the cells of the tumor to be positive for inhibin, Melan-A, synaptophysin, cytokeratin, and calretinin and negative for S-100 and chromogranin A. Notably, lipochrome and crystals of Reinke were not found in the tumor cells. Although the neoplasm fulfilled the criteria for a potentially metastasizing Leydig cell tumor, there was no evidence of that event having occurred, perhaps as a result of early treatment or as indication that criteria developed for Leydig cell tumor of adults may not apply to children.