Mixed germ cell tumor in the eye of a dog

A 3-year-old female neutered Staffordshire Bull Terrier presented with a mi xed germ. cell tumor involving the base of the iris and the ciliary body of the right eye. The tumor mass was composed primarily of packeted vacuolate d, polygonal (hepatoid) cells and small round cells; epithelial cells linin g tubuloacinar structures were a less prominent component. The hepatoid and round cells stained positively for alpha-fetoprotein and cytokeratin. The epithelial cells stained positively for cytokeratin only, and some containe d cytoplasmic mucin droplets. The polygonal cells were interpreted as a hep atoid variant of yolk sac tumor, and the epithelial cells were considered a teratomatous component. Trabeculae of bone were observed within the mass a nd may have been metaplastic or a teratomatous element. Extragonadal germ c ell tumors are rare in dogs and have previously been reported only in the s uprasellar region. This is the first report of this tumor type in the eye o f a nonhuman species.