Urethan Carcinogenesis in Newborn,Suckling,and Adult Mice of C57BL,C3H,BC3FJ,C3Hf,and SWR Strains

Urethan was given to four inbred strains of mice and to one hybrid, either in the drinking water at 0.4 per cent for 15–20 days to 5-week old animals, or subcutaneously 3 mg once to newborns, or intraperitoneally 1 mg/g body weight, 5 times, once every second day, to 10-day old animals. The 5 treatments starting at 10 days of age induced a high percentage of rapidly developing thymic lymphosarcomas, while in the groups treated at birth or at 5 weeks, few tumors of this type were observed. The incidence of non-thymic malignant lymphomas or leukemias was not influenced by urethan, apart from a reduction of latent period. A small number of mammary adenocarcinomas occurred among the treated females of the C57BL and SWR strains but none in the control groups. In C3Hf and BC3F₁ females there was a high incidence of mammary tumors when treatment was started at 5 weeks; treatment at birth or at 10 days did not modify the control incidence. On the contrary, hepatomas developed more rapidly and in higher percentage in the animals treated at birth or at 10 days. The incidence of pulmonary adenomas was increased by treatment in all strains parallel with the spontaneous occurrence. Tumors of harderian glands, skin, kidney, thyroid, adrenals and ovaries were also more frequent among treated animals.