Tumor Induction in Rats by Single Total-Body X-Irradiation

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Abstract
Female Holtzman rats were irradiated with a lethal dose of X-rays (700 r), protected by postirradiation parabiosis, and observed throughout their life span for late radiation effects. All irradiated rats surviving one year or more developed cataracts, and in about half of all exposed rats neoplastic growths were observed. Adenocarcinomas in axilla and groin probably derived from mammary glands accounted for more than half of the tumors, but sarcomas, carcinomas, and other tumors of various organs were also found. Croton oil increased the number of tumors in irradiated rats, but growth hormone and methylcholanthrene showed no co-carcinogenic effect. X-irradiation was primarily in the dose range which caused death by hematopoietic damage with minimal intestinal damage, and tumors were primarily non-intestinal. The hypothesis is presented that dose ranges or types of radiation which affect the intestine severely (1000 r X-rays; fast neutrons) induce intestinal tumors, whereas tumors due to lower X-ray doses (700 r) and gamma radiations, in which more rapid epithelial recovery occurs, are not of intestinal origin.