Ultraviolet B-induced tumors in pigmented hairless mice, with an unsuccessful attempt to induce cutaneous melanoma.

An animal experiment is presented in which pigmented hairless mice were exposed once per fortnight to high doses of ultraviolet B (UVB) to study tumorigenesis. The aim of the study was to confirm a causal relationship between cutaneous melanoma and UV radiation, and to find an animal model to study it. The experiment was based on the hypothesis that the risk of developing a melanoma is increased by a history of severe sunburns. Pigmented hairless mice, Skh-hr2, were exposed once every fortnight to high doses of UVB radiation from fluorescent sunlamps, Westinghouse FS40 T12. Heavy actinic damage was observed for several days after each exposure. Seventeen of the 24 animals eventually developed tumors. Histopathologically, 80% of the tumors were squamous cell carcinomas. Depositions of melanophages were observed, but no melanomas. In this mouse experiment no causal relationship between cutaneous melanomas and UV radiation could be established.