UV dose determines key characteristics of nonmelanoma skin cancer.

Basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), known as nonmelanoma skin cancer (NMSC), are the most common cancers worldwide. Although many factors are involved in the pathogenesis of NMSC, UV radiation is an important risk factor. A fundamental question in skin cancer research is whether varying doses of total UV radiation influence key characteristics of NMSC. The hypothesis that differences in UV doses influence the BCC/SCC ratio, number of tumors, and anatomic location of the tumor was investigated in 311 participants having 326 tumors and with exposure to a broad range of UV doses. An epidemiologic questionnaire was given to each participant soliciting detailed information on exposure to solar radiation. Environmental UVA and UVB doses were measured continually for 6 years at a permanent UV monitoring station. The total ratio of BCC/SCC was 3.5. Participants who received low and high UV doses had a BCC/SCC ratio of 4.2. Those who received very high UV doses had a ratio of 2.1. A very high UV dose was also associated with the doubling of the total number of tumors per person and a significantly increased risk of having SCC, a more aggressive malignancy. Tumors in sun-exposed areas (on the body) were more common in participants who received high and very high UV doses. The tumors in sun-protected areas were associated with exposure to lower levels of UV. This large-scale population study provides evidence that varying doses of UV radiation have a profound influence on key characteristics of NMSC.