Epidermal Carcinogenesis in the Mouse Induced by Applications of 7,12-Dimethylbenz-[a]anthracene Followed by Croton Oil

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Abstract
Three applications of 7,12-dimethylbenz[a]anthracene (DMBA) followed by repeated applications of croton oil induced about twice as many papillomas in mouse skin as did a single application of DMBA followed by croton oil. Varying the interval between the 3 applications of DMBA, within the limits of 1 day to 1 month, did not affect the yield of papillomas. The findings suggest that, contrary to earlier reports, the yield of papillomas induced in experiments of this sort varies with the dose of carcinogen. When a high concentration of DMBA was used, the papillomas appeared sooner after the beginning of croton-oil treatment with 3 applications of DMBA than with 1. This effect was lost if a weak solution of DMBA was used, or if the interval between the last application of carcinogen and the first of croton oil was extended to 14 weeks. It is suggested that the DMBA may have the same kind of promoting action as does croton oil.