Cancer in the Rat after Single Exposures to Irradiation or Hydrocarbons: Age and Strain Factors. Hormone Dependence of the Mammary Cancers

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Abstract
Single total-body X-irradiation (400 r) exerted selective cell damage in female rats. Hemopoietic tissues were damaged, and cancer was induced selectively in mammary gland and fibroblast. Among the undamaged tissues were pituitary, ovary, and vagina, which remained functionally intact, since regular estrus cycles persisted. The racial strain of origin of the rats had a profound influence on the development of mammary cancer after total-body irradiation. Females of the Sprague-Dawley strain developed both sarcoma and mammary carcinoma. In females of the Long-Evans strain, sarcomas were induced but mammary carcinoma was not observed. The tumors characteristic of each strain arose when irradiation was provided to neonatal (age 3 days) or adult rats. Mammary carcinoma was detected soon after irradiation, and sarcoma at a later time. In Sprague-Dawley females given a single total-body X-irradiation (400 r) at age 52 days, mammary carcinomas had the following characteristics: incidence in 29.7% of rats; 92% of the cancers detected within 79 days; multiple carcinomas found in 13% of cancerous rats. In sisters given two X-irradiations (400 r) at 52 and 92 days, mammary carcinomas had the following characteristics: incidence in 60% of rats; tumors detected in a continuous series from 25 to 220 days; multiple carcinomas in 26% of cancerous rats. A single intravenous injection of 5 mg of 7,12-dimethylbenz (a) anthracene, was more efficient than X- irradiation (400 r) in induction of mammary cancer; incidence, 100%; rats with multiple tumors, 68%. A newly recognized property of radiation-induced mammary carcinoma of rat is hormone dependence of the cancers. Mammary carcinomas in Sprague-Dawley rats, induced by radiation or by polycyclic aromatic hydrocarbons, shared the following qualities: similar histological appearance; similar regressive properties after ovariectomy; similar content of five dehydrogenases[long dash]glucose-6-phosphate, 6-phosphogluconic, isocitric, lactic, and malic.