This study was aimed at examining the incidence and histological type of the breast tumors of rat induced by 60Co γ-ray irradiation. Twenty Sprague-Dawley rats were given 0.9Gy of 60Co γ-ray for 6 weeks (0.15 Gy per week), and were killed 46
weeks
after the end of irradiation. Juvenile fibroadenoma(JFA) was the most frequent tumor(18 of 20), and adenoma(2 of 20) was the second frequent one. The 18 cases of JFAs showed broad spectrum of morphologic changes. The 2 cases revealed massive
fibrosis of
intralobular stroma(JFA with massive fibrosis), the 6 cases typical JFA, the 6 cases showed focal alveolar hyperplasia(JFA with focal alveolar hyperplasia), and rest 4 cases showed diffuse alveolar hyperplasia(JFA with diffuse alveolar
hyperplasia).
Although the rats were not pregnant nor lactating, 2 cases of adenoma were morphologically identical with lactating adenoma. These results suggest that the responsiveness of breast tissue to the radiation is different even in the same species of
animals. JFA can be easily made in Sprague-Dawley rats by 60Ca γ-ray irradiation, and this method can be used as a good experimental model in studying the JFA.
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