Urethan (ethyl carbamate) alone is carcinogenic for mouse skin

Nine groups of 32 hairless mice (16 males and 16 females in each) were painted on the back skin with approximately 200 microliters solution of urethan twice a week for up to 58 weeks. The following treatments were given: acetone alone, propylene glycol alone, 10% urethan in acetone, 15% urethan in propylene glycol, 20% urethan in acetone, 30% urethan in propylene glycol, 40% urethan in acetone, 75% urethan in propylene glycol, and approximately 100% melted urethan. Histological examinations revealed no development of general epidermal hyperplasia or inflammatory reactions. Tumors developed in skin, liver and lymph nodes, and one mouse also developed leukemic infiltrations in kidneys and lungs. The rate and yield of skin tumors were registered and statistically analyzed. The number of other tumors occurring was also recorded. The results confirm that urethan is a tumorigen for the lung and several other organs, and that it is also a complete carcinogen for hairless mouse skin, even in a dose as low as 10% urethan in acetone. There is also a significant dose-response relationship.