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The Promoting Action of Croton Oil in Skin Tumorigenesis^*

( Cancer Research Laboratory, University of Florida, Gainesville, Fla.)

Strain DBA mice were painted once on both ears with methylcholanthrene. Approximately 2 weeks thereafter, croton oil was applied to the same site. Although few or no tumors were observed following 1, 5, 10, or 20 paintings with croton oil, a definite co-carcinogenic effect was obtained when the number of applications was increased to 30.

When croton oil was painted continuously during an extended interval and, following a rest period, this was repeated, it was observed that the first series of paintings had little influence on the second in promoting the development of visible tumors.

Croton oil was more effective as a promoter when applied continuously rather than intermittently and when applied 2 times as against 3 times per week.

^* This investigation was supported by research grant C-1709 from the National Cancer Institute of the National Institutes of Health, Public Health Service, and the Damon Runyon Memorial Fund.

Received 12/20/52.

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