Re: Sun exposure and mortality from melanoma.

The relationship between sun exposure and melanoma mortality and risk of lymphoma was explored in two recent articles and a related editorial ( 1 – 3 ) . Unfortunately, the discussion in the related editorial ( 1 ) was not supported by the data presented. The study by Berwick et al. ( 2 ) demonstrated, within the limits of a retrospective study, that patients with melanoma have a better prognosis if they had previous extensive sun exposure. The indices of sun exposure refl ected many years of exposure dating to youth and did not relate to exposure in the interval after diagnosis of melanoma. No data on vitamin D levels were provided. The data strongly suggested that melanomas induced by intense sun exposure have a more benign behavior than those not induced by intense sun exposure. This is the most direct explanation for increased survival from melanomas arising in patients with a history of intense sun exposure and is analogous to experience with other sun-induced cancers. Squamous cell carcinomas of the skin induced by sun have a much better prognosis than squamous cell cancers arising in scars. This relationship between melanoma survival and sun exposure may explain the stable melanoma mortality rate despite an increase in incidence in sun – induced melanoma and has consequences for public health. Data in the article by Smedby et al. ( 3 ) suggest that participants who had extensive sun exposure had a decreased lymphoma risk compared with participants with less sun exposure. However, there was an exception for patients with a prior history of skin cancer. Thus, lymphoma risk was elevated in patients with skin cancer plus extensive sun exposure and decreased in patients with extensive sun exposure without skin cancer. This difference in risk cannot be explained by vitamin D levels because vitamin D levels should also be elevated in patients with extensive sun exposure and skin cancer. The data suggest that suninduced skin cancer is simply a marker for a decreased ability to handle carcinogenic insult. The skin cancer data confl ict with a direct link between sun exposure and lymphoma risk or a role for vitamin D. This problem with the analysis, which attributed the results to vitamin D levels, is not without consequences because it would lead to the recommendation that people increase their exposure to a carcinogen.