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Summation and Inhibition Effects of Weak and Strong Carcinogenic Hydrocarbons: 1:2-Benzanthracene, Chrysene, 1:2:5:6-Dibenzanthracene, and 20-Methylcholanthrene^*

(From the Department of Pathology, University of Chicago, Chicago 37, Ill.)

1. 1:2-Benzanthracene and chrysene were carcinogenic, inducing sarcoma on subcutaneous injection. The former was stronger than the latter, having both a shorter induction time and a higher tumor yield. The significance of these results with regard to the relation of chemical-physical characteristics of hydrocarbons to their carcinogenicity is discussed.

2. 1:2-Benzanthracene and chrysene injected together showed definite summation of carcinogenic effects if not actually a synergistic action. The tumor yield was greater than the sum of their individual tumor yields, despite the halving of the dose of each compound injected. This observation is significant, because it cannot be explained by the existing theories of inhibition or summation effects of carcinogenic compounds.

3. The carcinogenic effects of 1:2-benzanthracene and 1:2:5:6-dibenzanthracene injected together were not those of summation but apparently of inhibition.

4. The carcinogenic effects of 1:2:5:6-dibenzanthracene and 20-methylcholanthrene injected together were additive, although imperfectly so.

^* This investigation was aided by a research grant from the American Cancer Society, on recommendation by the Committee on Growth of the National Research Council.

Received 8/30/50.