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Epidermal Carcinogenesis in the Mouse Induced by One, Two, or Three Applications of 9,10-Dimethyl-1,2-benzanthracene Followed by Repeated Applications of Croton Oil. A New Hypothesis of the Mechanism of Carcinogenesis^*

Philippe Shubik and A. C. Ritchie

( Division of Oncology, The Chicago Medical School, Chicago 8, Ill.)

1. C3H male mice received either one, two, or three skin applications of a 1.0 per cent solution of 9,10-dimethyl-1,2-benzanthracene followed by croton oil repeatedly. No differences in the tumor incidences were noted.

2. Swiss female mice received either one, two, or three skin applications of a 0.2 per cent solution of 9,10-dimethyl-1,2-benzanthracene followed by croton oil repeatedly. Decreasing numbers of tumors were recorded with increasing numbers of applications.

3. The possible significance of these findings is discussed. The secondary necrotizing action of carcinogenic hydrocarbons and the possible induction of a refractory state are considered as explanations.

^* This work was supported by research grants from the National Cancer Institute of the National Institutes of Health, Public Health Service, Bethesda, Md.

Present address: Massachusetts General Hospital, Boston, Mass.

Received 11/20/52.