Sun exposure and the epidemiology of melanoma and melanocytic nevi (Moles)

Epidemiological studies suggest that sun exposure is a common etiologic factor for both melanocytic nevi (benign tumors of the pigment producing cells in the skin; better known as moles) and melanoma (Armstrong and English 1992). \ud \ud The role of sunlight in the pathogenesis of melanoma was first proposed by McGovern (1952). Since then, more than 30 case-control studies have examined the role of sun exposure in the development of melanoma (Elwood and Gallagher 1994) resulting in substantial evidence implicating sunlight as the principal environmental cause of melanoma in white-skinned populations (IARC 1992). However, the dose response relationship appears to be quite complex (Fitzpatrick 1989).\ud \ud Interest in melanocytic nevi stems from their clinical, histological and epidemiological association with malignant melanoma. Numerous case-control studies have shown that the number of melanocytic nevi is the strongest phenotypic risk factor for melanoma (Armstrong and English 1992). Similar to melanoma, melanocytic nevi appear to have a complex relationship with sun exposure, and are also associated with phenotypic markers of sun-sensitivity (Armstrong and English 1988). \ud \ud The ultraviolet wavelengths of the electromagnetic spectrum appear to be the most relevant to the pathogenesis of melanoma (Diffey and Elwood 1994). UVA (315-400 nm), UVB (280-315 nm) and UVC (100-280 nm) radiation are all considered to be potentially carcinogenic to humans (IARC 1992), and their ability to induce skin damage is thought to be inversely related to wavelength (Marrett 1994). The known adverse effects of UVA and UVB include erythema, skin thickening, photoaging, photosensitivity reactions, melanocyte proliferation, DNA damage, inhibition of DNA repair, immunosuppression and carcinogenesis (Marrett 1994). However, the strength of these effects and the level of penetration into the skin varies between these two wavebands (Marrett 1994). As the UVC component of sunlight does not reach the earth’s surface, only non-solar sources such as arc welding equipment present a problem (Marrett 1994). \ud \ud As the etiology of melanocytic nevi has been under investigation for a shorter period of time than melanoma, numerous questions remain to be answered (Armstrong and English 1988). However, there are many epidemiologic observations linking solar UVR to the development of acquired melanocytic nevi