Urethan (ethyl carbamate) is an effective promoter of 7,12-dimethylbenz[a]anthracene-induced carcinogenesis in mouse skin two-stage experiments

Groups of hairless mice were painted with urethan alone, with the complete carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) alone, and with an initiating dose of DMBA followed by continual treatment with urethan or with the promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). The animals were examined once a week for an appropriate time period. Malignant and non-malignant skin tumors were registered and classified. Lung adenomas and other internal tumors were also counted. The results show that all types of treatment produced skin tumors, some of which were malignant. When urethan was used lung adenomas also appeared, along with a few other tumors. The results show that a 10% solution of urethan in acetone is a significant promoter, showing synergistic increase of DMBA-induced skin tumors, but urethan is not as strong a promoter as 10 nmol TPA. Urethan is said to be the pure initiator of skin carcinogenesis. Previously the author has shown that urethan alone is a complete carcinogen and here it is shown that it is also a promoter. Hence, the current hypothesis of urethan as a pure initiator in skin carcinogenesis has been disproved.