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Comparison of lung tumorigenesis induced by urethan in athymic nude mice and euthymic littermates.

Athymic (nu/nu) and euthymic (nu/+) mice were intraperitoneally given doses of 0.25 to 1.5 mg/g body weight of urethan at the age of 14 to 16 days. Dose-response relationship and sequential changes in lung tumorigenesis induced by urethan in athymic mice were compared with those in euthymic littermates. The urethan dose-response relationship in lung tumorigenesis of the nu/nu mice was almost the same as that in the nu/+ mice. Incidence and multiplicity of the lung tumors were investigated sequentially 28 days to 12 months after urethan injection. They showed similar indexes in the two phenotypically different mice at varying periods after 0.5 mg/g body weight urethan treatment (incidences of 4.8 and 4.4 tumors/mouse and 96 and 97% for nu/nu and nu/+ mice, respectively, at 12 months after treatment). This means that the length of the latent period is similar in these phenotypically different mice. It may be concluded that the immunosurveillance mechanism mediated by T-cells does not function in the present model.