Tumor induction in sencar mice in response to ultraviolet radiation

The purpose of this study was to ascertain whether Sencar mice, which are extremely susceptible to two-stage skin carcinogenesis by chemical carcinogens, also exhibit increased susceptibility to carcinogenesis by ultraviolet radiation (UVR). Sencar and CD-1 mice were given a single treatment of UVR from FS40 sunlamps and received no subsequent treatments with chemical or physical promoters. The doses administered were 0, 2.88, 5.76, or 11.52 × 10⁴ J/m². No tumors were observed in either treated or untreated CD-1 mice at 30 weeks after irradiation. Papillomas began to appear at 6 weeks after irradiation in Sencar mice; the cumulative incidence of tumors at 30 weeks after irradiation was 40 and 45% for the two highest UVR dose groups. Approximately 50% of the tumors regressed spontaneously. In several cases, however, the remaining tumors progressed to squamous cell carcinomas. These results indicate that the hypersensitivity of Sencar mice to tumor induction in skin exists not only with respect to chemical carcinogens but also with respect to at least one physical carcinogen (UVR).