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Carcinogenesis of the Skin. A Re-examination of Methods for the Quantitative Measurement of the Potencies of Complex Materials^*

( Kettering Laboratory, Department of Preventive Medicine and Industrial Health, College of Medicine, University of Cincinnati, Cincinnati, Ohio)

1. Data are presented to indicate the hazards of attempting quantitative comparisons of the results of experiments in which satisfactory growth of the mice does not occur.

2. Satisfactory tests may be compared on the basis of the relative rates at which papillomas are induced. The rates are related through external reference standards involving solutions of 3-methylcholanthrene (MC) in benzene. Thus, the Relative Carcinogenic Potency, PMC, of any given complex oil is defined as the concentration of MC which will produce tumors at the same rate as the oil under comparable experimental conditions.

3. Correlation of data from tests involving the application of MC in benzene to C3H mice yields the following relationship: where is the mean time of appearance of tumors and d the dosage of MC applied per unit area of the skin each week.

4. The relative potencies, P, of 7,12-dimethylbenz[a]anthracene, 3-methylcholanthrene, and benzo[a]pyrene for the skin of C3H mice are approximately 160, 100, and 50, respectively.

5. The rate of induction of tumors by MC in benzene and in some oils is independent of the quantity used for each application, over the range of 10–100 mg. However, certain oils induce tumors much more rapidly if 100 mg. is applied each time than if 10–20 mg. is used.

^* The majority of this work was carried out as part of the American Petroleum Institute Research Project MC-1.

Received 12/ 3/54.