An UVB-carcinogenesis model with KSN nude mice.

We established and characterized a systematic ultraviolet light-induced carcinogenesis model using KSN nude mice. We prepared five groups of KSN mice and exposed them six times a week to five levels of daily ultraviolet B (UVB) doses; 1340, 670, 320, 160 and 0 J/m2/day. In 670, 320 and 160 J/m2/day, the latency period tended to become shorter in proportion to the daily doses and prevalence data fitted well to log-normal distribution. In the log-log plot of days till 50% prevalence versus daily dose, we saw a linear relationship for 1 mm tumor diameter. From this analysis, we determined that days necessary to reach 50% prevalence is in proportion to the -0.49 power of daily dose. The average number of tumors per survivor correlated with prevalence data. Direct measured rates of tumor growth were independent of daily UVB-dose. Therefore we speculated that UV-irradiation did not affect tumor growth after its appearance. Most UVB-induced tumors were squamous cell carcinoma, the rest were spindle cell carcinoma, papilloma and mixed type. We concluded that our experimental data with nude mice was in accordance with data with hairless mice in nature.