Spontaneous seminoma in an owl monkey in captivity.

An adult male Aotus nancymae maintained for breeding purposes was submitted for surgery and the left testicle was removed. The surgically removed mass was about two to three times the size of a normal adult owl monkey testicle. Grossly, on cut surface, the mass was soft, white to pale gray, and bulged above the adjacent tissue. Microscopically, the morphology of the tumor cells was consistent with a seminoma.