Lung Carcinogenesis During in Vivo Cigarette Smoking and Radon Daughter Exposure in Rats

Abstract

The carcinogenic activity of tobacco smoke is clearly demonstrated by human epidemiologic data. Whereas in experimental animals tracheobronchial applications or injections of tars produce cancerous lesions, inhalation exposure to tobacco smoke only induces benign tumors of the bronchial epithelium and lung parenchyma [8]. The failure to induce, in animals, malignant lung tumors with inhaled cigarette smoke seems to be due to the chemical toxicity of the components of tobacco smoke. In particular, carbon monoxide and nicotine make it impossible to use the amount of inhaled smoke which would be required to induce malignant lung lesions during the relatively short life span of rodents. Since tobacco smoke is rarely inhaled alone by humans, but usually in association with other physical or chemical pollutants, we undertook experiments in which tobacco smoke was administered as a cocarcinogen to rats previously exposed to inhalations of radon and its daughter products.