Ultraviolet radiation and malignant melanoma

Abstract

Electromagnetic radiation from the sun is divided into three regions: ultraviolet (UV), visible, and infrared. The UV spectrum is further subdivided into UVA (320400 nm), UVB (290-320 nm), and UVC (200-290 nm). Solar energy in the UVC range is completely absorbed by the ozone layer, and thus it does not reach the Earth’s surface.3 Although epidemiologic evidence supports the notion that sunlight is germane to the development of cutaneous melanoma, the precise action spectrum for melanoma formation is still unknown. For nonmelanoma skin cancer, UVB appears to be the most carcinogenic.” What is the evidence for UVB’s involvement in melanoma? First, UVB can be absorbed by DNA, leading to mutations and cellular transformation. Second, UVB can stimulate melanocytic proliferation. Third, UVB is immunosuppressive in mice and can lead to diminished tumor resistance. Fourth, blistering sunburns are caused by UVB and represent a risk factor for melanoma. Lastly, melanoma incidence correlates directly with UVB flux and gradients of UVB by latitude.” Absorption of UVB energy by DNA leads to photoproducts such as pyrimidine dimers.6 If DNA repair is not properly executed, mutations in critical oncogenes, such as the ras oncogene, can lead to uncontrolled melanocyte proliferation and eventual tumor formation.7,8 Likewise, UVB may also interfere with normal functioning of tumor-suppressor genes, thereby inducing melanoma. A group of investigators has shown that UVB-