Experimental carcinogenesis. Bronchial intramural adenocarcinomas in rats from x-ray irradiation of the chest.

Abstract

One hundred eighty-six rats and 202 hamsters, that survived the respective time periods when the first lung cancer was diagnosed in each species, had been given an exposure of 3000 R or 4000 R of x-irradiation applied externally to the chest. About 43% of the rats, but only 2% of the hamsters, developed lung cancer. To enhance the prevalence of lung cancer, some of the irradiated animals were injected intratracheally with 9, 10-dimethyl-1, 2-benzanthracene (DMBA). Lung cancer prevalence in irradiated animals injected with DMBA was no higher than that in irradiated animals not so injected. Intratracheal injections of DMBA in nonirradiated rats did not result in tumor production but, in nonirradiated hamsters, DMBA caused a 6% prevalence of lung cancer. The mortality rate of both animal species showed a more than additive effect in animals given the higher x-ray dosage plus intratracheal injections of either DMBA or iron oxide alone. The lung cancers in the irradiated rats predominantly affected bronchi (86%) and were mostly adenocarcinomas (88%). The cancers were generally intramural and were covered by an intact and normal surface epithelium. Their origin appeared to be from aberrant intramural glands. These glands are not found in the bronchi of germ-free rats but do occur in bronchi thickened by severe endemic chronic bronchitis.