Spontaneous tumours in C3H-Avy and C3H-AvyfB mice: High incidence in the United States, low incidence in Australia

C3H-Avyy and C3H-Avy, fB mice, with a virtual 100% incidence of liver and mammary tumors in the United States, had an almost 0% incidence of these tumors when these mice were bred and reared in Australia, particularly after the first generation. C3H-Avymice, when reared in Australia but provided with U.S. feed and bedding (cedar shavings), also had essentially a 100% incidence of mammary tumors. Although our results did not rule out other possibilities, the implication of cedar as a "carcinogenic” agent was quite clear-cut. These observations, although not yet made on large numbers of mice, provide new parameters for the study and understanding of the development of spontaneous mammary and liver cancer in mice.—J Natl Cancer Inst 50: 1237-1242, 1973. © 1973 OUP Publishing Ltd.