Abstract
Purpose::
There is accumulating evidence that vitamin D is a protective factor in the pathogenesis of many cancers. We evaluated the influence of ultraviolet radiation (UVR) exposure, a surrogate measure of vitamin D exposure, on survival in patients with ocular melanoma.
Methods::
A consecutive series of 2003 patients, diagnosed with uveal melanoma and treated with proton therapy between 1975 and 1986, were included in the analysis. Patients were followed through June 1999, with a median follow up among surviving patients of 10.0 years. A UVR score corresponding to each patient’s place of residence at the time of diagnosis was used as a measure of vitamin D-inducing UVR exposures. The UVR score is based on satellite imagining and ground level monitoring at stations throughout the US (http://www.cpc.ncep.noaa.gov/ products/stratosphere /uv_index). UVR index values range from low (2 or less) to extreme (12 or higher), and take factors which influence ground-level UVR, such as latitude, altitude and cloud cover, into account. Higher (erythemal) UVR levels are associated with a greater capacity for endogenous vitamin D synthesis. Cox regression analysis was performed to examine the relationship between UVR and melanoma-related mortality, while adjusting for established prognostic factors.
Results::
Overall, we observed no relationship between UVR score and mortality from eye melanoma. However, further analyses revealed strong interaction by iris color (P interaction=0.005), a surrogate for propensity to sunburn. Whereas higher (vitamin D-inducing) UVR scores were associated with a nonsignificant increase in death rates among lighter eyed persons (P trend for UVR score: P=0.05), a strong protective association was observed among persons with a darker iris. When compared to low ambient UVR (UVR scores<3), UVR scores of 6 or greater were associated with a significant 62% reduction in melanoma death rates (RR: 0.38; P=0.005) among brown-eyed persons. The inverse association was consistent in men (RR: 0.47; P=0.11) and women (RR: 0.26; P=0.02).
Conclusions::
These findings provide some support for the hypothesis that vitamin D from sunlight exposure is a protective factor in the pathogenesis of eye melanoma.
Keywords: melanoma • clinical (human) or epidemiologic studies: risk factor assessment • radiation damage: light/UV