Testicular Yolk Sac Carcinoma in an Aged Sprague-Dawley Rat

A spontaneous yolk sac carcinoma derived from the testis of an old male Sprague-Dawley rat was examined morphologically. The tumor was composed of cuboidal cells arranged into small groups or forming single cell rows. The tumor cells had round to oval, single central or polar nuclei with amphophilic, granular, finely vacuolated cytoplasms. The intercellular spaces contained large amounts of basement-membrane-like, eosinophilic matrix. This matrix was stained positively for laminin and periodic acid-Schiff (PAS). Some visceral cysts were lined with well differentiated cells, flat or cuboidal vacuolated epithelium. An ultrastructural examination showed that the hyaline matrix of the tumor had a finelamellar structure. These morphological characteristics in our case strongly suggest that this tumor is a yolk sac carcinoma, being similar to experimentally induced ones. No report of spontaneously occurring yolk sac carcinoma derived from rat testis was found in the literature. (J Toxicol Pathol 1998 ; 11 : 203～204)