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The Effect of Long Ultraviolet Radiation on the Development of Tumors Induced by 20-Methylcholanthrene

( Department of Environmental Medicine, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Md.)

When mice are exposed to a moderate dose of long ultraviolet radiation (4–8 x 10⁷ ergs/sq cm), immediately after painting with 20-methylcholanthrene, the rate of papilloma development is accelerated. Within these limits increasing the amount of radiation increased the acceleration. There was no effect on the rate of carcinoma development.

When prolonged radiation was given (10–18 x 10⁷ ergs/sq cm), there was an initial acceleration of papilloma development, but the early tumors regressed so that, eventually, the rate of tumor development in radiated groups was slower than in the controls. In addition, there was a retardation of the carcinogenic process.

Received 6/ 3/63.