Studies on Radiation-Induced Mammary Gland Neoplasia in the Rat: III. Relation of the Neoplastic Response to Dose of Total-Body Radiation

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Abstract
The dose dependency of the breast neoplasia response was studied in female Sprague-Dawley rats exposed to graded doses of acute total-body radiation at 40 days of age. The incidence of neoplasia scored at 10.5 to 11 months was linear on doses between 25 r (the lowest dose studied) and 400 r. The extrapolated curve passed through zero incidence at zero dose. Above 400 r, the incidence either remained constant or decreased. Multiple neoplasms in single animals observed were adenocarcinomas, adenofibromas, fibroadenomas, and fibrosarcomas. The neoplasms depend on intact ovarian function for maximal incidence. The dose-effect results are discussed in terms of their adequacy for interpretation in terms of the mechanism of radiation-induced neoplasia. The data reported on the relation of dose and neoplasia of the rat breast cannot be extrapolated to other types of neoplasia or to other species. The linearity of response for a given tissue might be masked by dependence of the response on hormones or other factors in addition to radiation.