Factors modifying experimental epidermal carcinogenesis in mice.

brought to visible tumors. Mottram (10) observed tumor production in mouse skin after exposing it to a single treatment with a carcinogenic hydrocarbon, followed by re peated applications of croton oil. Later, Berenblum and Shubik (3) adapted this method to a quantitative approach to the study of chemical carcinogenesis. According to this method, the actual number of tumors produced were said to measure the initiating potency of the substance under test, while the latent period constituted a measure of promoting activity. Thus, when equal amounts of two or more different carcinogens are used for the primary treatment, followed by a standard course of croton oil applications, their respective initiating potencies can be compared (3, 7). Conversely, if different concentrations of the same carcinogen are utilized, the relationship between dose and tumor response may be studied. Berenblum and Shubik have demonstrated a direct relationship between the amount of the ini tiating dose and the tumor response in mice, using several concentrations of 9,10-dimethyl-l,2-benzanthracene (4). Shubik and Ritchie (14) have extended these experiments by applying the in creased amounts of carcinogen in the form of two and three applications, with a time interval of 7 days between each, croton oil treatment com mencing 5 weeks after the initial application of DMBA. Repetition of the initiating dose in this manner resulted in an equal or even a lower tumor response than that obtained from the single appli-