The effect of application frequency on epidermal carcinogenesis assays

Classic mouse skin-painting assays of such highly-complex mixtures as petroleums and synthetic fuels may lead to severe local cytotoxic effects that can alter tumorigenesis. This effect can be particularly disruptive in dose-response studies where a wide range of doses is employed. The experiments described here illustrate that frequency of exposure may be more important than the concentration of individual doses. C3Hf/Bd mice were exposed to 2 shale oils in experiments in which a constant weekly dose was either applied once or divided into 2 or 4 equal parts and applied either twice or 4 times each week. In experiments with either oil, a single weekly application was more effective in total tumor production and less cytotoxic than more frequent application of less-concentrated doses.