SUMMARY Spontaneous Tumors In Germ-Free Rats 1. 2

Three strainll of gel'Dl-free rats were exanlined for evidence of spontaneous neoplasms. None was observed in gel'Dl-free rats derived from Fischer and Sprague-Dawley stock. Twenty-five tumors were recorded in gel'Dl-free rodents of Wistar strain origin, the majority of which involved the mam-mary gland.-J Nat Cancer Inst 31: 457-465, 1963. SOME STRAINS of laboratory-propagated rats develop spontaneous neoplasms, coincident with aging. While vague in etiology, the majority of them involve the mammary gland (1-4,), The tumors range in his-tological types from benign adenofibromas to malignant adenocarcinomas; some of the latter have metastases. The rats propagated and maintained under germ-free conditions at the Lobund Laboratory have been observed carefully during the past 8 years for evidence of neoplastic disease. The majority of tumors thus detected involved the mammary gland in rats only of Wistar strain origin. MATERIALS AND METHODS Three strains of rats are being propagated under germ-free conditions at Lobund Laboratory: Wistar, Fischer, and Sprague-Dawley. The Wistar strain was derived from cesarean-delivered litters, hand-fed on sterile diet until weaned, and has now been propagated by random matings up to the twentieth generation. The Fischer strain was derived from cesarean-delivered litters, foster-nursed on germ-free Wistar strain rats, and has been propagated up to the ninth generation by random mating. The Sprague-Dawley strain was similarly derived and foster-nursed on germ-free Wistar rats and has been propagated in germ-free status up t