Can ultraviolet radiation act as a survival enhancer for cutaneous melanoma?

Some studies have suggested that sun exposure plays a protective role in melanoma survival. This created a paradox as the known carcinogen can act as a cancer promoter and also as a survival enhancer. The aim of this study was to investigate the effect of sun exposure on melanoma mortality using both ambient sun exposure and individual data. A 10-year cohort study was carried out on primary cutaneous melanoma cases (n=972). Residential data were coupled with levels of ultraviolet radiation (UV) to provide a measure of individual exposure. Demographic, histological and clinical data were obtained for all participants. In a subsample, information on pigmentary characteristics, diet, medical history, phenotype and self-reported sun exposure was also collected. Survival analysis and Cox proportional hazards models were used to examine associations. No protective effect was found for UVB or individual sun exposure variables on melanoma mortality. However, an increased risk of mortality was found among patients with cutaneous melanoma located on the lower limbs and in the highest decile of UVB exposure (≥3.298 J/cm) after controlling for sex, age and Breslow thickness (relative risk: 4.78; 95% confidence interval: 1.30-17.5). The increased risk of mortality for the highest decile of UVB was also confirmed in the subsample after controlling for sex, age, education, use of sun lamps, pigmentary characteristics and diet. The results of the study suggested no protective effect of sun exposure for melanoma mortality and showed that high sun exposure increases the risk of melanoma mortality among patients with melanomas located on the lower limbs.