Intracisternal virus-like particles in two guinea pig mammary adenocarcinomas

Virus-like particles were found in spontaneously arising mammary adenocarcinomas from 2 male guinea pigs. The type-B particles were 100 nm in diameter and budded from the apex of stalks into cisternae. Examination of normal and neoplastic tissues from other guinea pigs failed to reveal similar particles. A review of the literature revealed that of the 16 known cases of mammary adenocarcinomas in guinea pigs, 5 have occurred in male animals. The apparent propensity for spontaneous mammary adenocarcinomas in males of this species is discussed in relation to the possible etiologic agents responsible for them.