@article{oai:repo.qst.go.jp:00044130,
 author = {Imaoka, Tatsuhiko and Nishimura, Mayumi and Nishimura, Yukiko and Kakinuma, Shizuko and Shimada, Yoshiya and 今岡 達彦 and 西村 まゆみ and 西村 由希子 and 柿沼 志津子 and 島田 義也},
 issue = {3},
 journal = {In Vivo},
 month = {May},
 note = {Background: The rat model of radiation-induced carcinogenesis is widely used to estimate breast cancer risk, but it is unknown whether mammary terminal end buds (TEBs), the hypothesized target of chemical carcinogens, are also targets of radiation-induced carcinogenesis.
Materials and Methods: Female Sprague-Dawley rats were irradiated with X-rays (2 Gy). The morphology, bromodeoxyuridine (BrdU)-labeling index and pyknotic index of mammary ductal termini were investigated from 6 hours to 8 weeks post-irradiation. 
Results: Irradiated rats showed a significantly smaller decrease in TEB numbers than controls 4 weeks after irradiation. The BrdU-labeling and pyknotic indexes initially decreased and increased, respectively, recovered to control levels by 3 days post-irradiation, and remained significantly higher until 8 weeks and at 4 weeks post-irradiation, respectively. One case of ductal hyperplasia was observed at 8 weeks. 
Conclusions: Irradiation resulted in a persistent proliferation of TEBs, which may be associated with neoplastic transformation via a temporal differentiation arrest.},
 pages = {353--358},
 title = {Persistent cell proliferation of terminal end buds precedes radiation-induced rat mammary carcinogenesis},
 volume = {20},
 year = {2006}
}