According to Armstrong and Kricker (1996), at least six major lines of evidence support the proposition that sun exposure causes skin cancer (Table 12.3). Interestingly, the publication on sunlight and skin cancer of the International Agency for Research on Cancer (IARC) (1992) argues that the evidence was sufficient for both melanoma and nonmelanoma skin cancer (basal and squamous cell carcinomas of the skin), but was more substantial in support of a causative relationship between sun exposure and melanoma development. This is somewhat surprising in view of considerable literature, both before and after the IARC report, that does not indicate such a certain relationship between UV radiation and melanoma development (Ur- bach, 1997; Leffell and Brash, 1996; Elwood, 1996). In any event, there is no question that UV
Table 12.3 Categories of Epidemiological Evidence for the Causation of Skin
Cancer by Sun Exposure
1. Skin cancers are more frequent in residents of areas of high ambient solar radiation.
2. Skin cancers are more frequent in sun-sensitive people.
3. Skin cancers occur mainly on sun-exposed areas of the body.
4. Skin cancers are more frequently seen in people having high sun exposure.
5. Skin cancers are more frequent in people with benign sun-related skin conditions.
6. Skin cancers are less likely to occur where the skin is protected against solar radia- tion by a variety of means.
Adapted from Armstrong and Kricker, 1996.
radiation in sunlight plays a major if not the predominant role in the development of skin cancer in the human.