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Factors Modifying Experimental Epidermal Carcinogenesis in Mice^*

S. D. Vesselinovitch and J. P. W. Gilman

( Division of Biology, Ontario Veterinary College, Guelph, Canada)

1. Mice were treated with either single applications of a 1.5 per cent solution of 9,10-dimethyl-1,2-benzanthracene (DMBA) or two such applications separated by a 30-day interval.

2. In all groups the initial treatment was followed by 33 applications of croton oil, beginning either on the 7th or 40th day after the first DMBA exposure.

3. The time lapse between the initiating treatment with the carcinogen and commencement of promoting treatments with croton oil did not affect either the number of tumors or the latent period in groups exposed only once to DMBA.

4. Two exposures to DMBA, when separated by a 30-day interval, resulted in an increase in the number of tumors, but there was no appreciable alteration in the percentage mice developing tumors.

5. An even greater increase in the number of tumors was obtained when ten croton oil paintings preceded the second DMBA exposure.

6. The significance of these findings were discussed in connection with the initiation-promotion concept of the process of carcinogenesis.

^* This work was supported in part by a grant-in-aid from the National Cancer Institute of Canada.

Research Associate Fellow, National Cancer Institute of Canada.

Received 8/20/56.