© 2005 Oxford University Press
CORRESPONDENCE |
RESPONSE: Re: Sun Exposure and Mortality From Melanoma
Affiliations of authors: Vanderbilt University School of Medicine and Vanderbilt-Ingram Cancer Center, Nashville, TN (KME, JAS, WJB); International Epidemiology Institute, Rockville,MD (WJB)
Correspondence to: Kathleen M. Egan, ScD, Vanderbilt University School of Medicine, Department of Medicine, Medical Center East, Suite 6000, Nashville, TN 37232–8300 (e-mail: Kathleen.Egan{at}Vanderbilt.edu).
Our editorial raised the question of whether vitamin D might account for findings in two reports published in the Journal (1,2) that suggested a beneficial impact of sun exposure on the incidence of malignant lymphoma, and outcomeof skin melanoma (3). The authors ofboth manuscripts, and of a third study that we cited, which had similar findings for non-Hodgkin lymphoma (4), all raised the question of whether vitamin D could account for the apparent salutary influence of sunlight. In his letter, Dr. Kalish indicated some legitimate questions regarding that interpretation, as did we in our editorial. We pointed out that the findings of Berwick et al. (1) applied to sun exposures predating the melanoma diagnosis, and we, like Kalish, suggested that the finding could be due to a more benign behavior of melanomas arising on chronically sun-exposed skin.
In support of the "most direct" explanation for the findings by Berwick et al., Dr. Kalish speculates that "...This relationship between melanoma survivaland sun exposure may explain the stable melanoma mortality rate despite an increase in incidence in sun-induced melanoma...." Although this may be one explanation for the stable mortality rate, it is more likely a product of increased awareness and earlier detection. In the last several decades in the United States, an increasing proportion of melanomas have been diagnosed at a localized stage or as thin lesions, whereas the diagnosis of ulcerated poor-prognosis melanomas has declined (5). Corresponding with these trends, 5-year survival rates in melanoma statistically significantly improved from 1975 to 2000 (6).
Kalish cites the result in the article by Smedby et al. (2) that a history of nonmelanoma skin cancer was associated with an increased risk of lymphoma as evidence against a hypothesis related to vitamin D. The results of Smedby et al. (2) indicated an inverse association with lymphoma for sunbathing, sunburns, and sunny vacations, and a positive association for nonmelanoma skin cancer. Clearly, these results are difficult to reconcile by one common mechanism. Considering this evidence, it seems likely that lymphomas—like melanomas—may arise through several pathways. Risk associated with a past history of skin cancer (reported by 4% of the case patients) is consistent with a role for a genetic variation in DNA repair efficiency or the immunosuppressive properties of UV radiation as discussed by Smedby et al. (2) and Hughes et al. (4). The observation in two recent reports (2,4) of an inverse association related to periodic sun exposure suggests at least one additional mechanism through which sunlight might act. Whether this mechanism is related to vitamin D or some other correlate of sun exposure must still be sorted out.
No one, including the authors of the two reports, is suggesting that sunbathing is the route to cancer avoidance or to a better cancer outcome. However, the hypothesis that vitamin D—which can be obtained in supplement pills and diet, as well as through sun exposure—may act to prevent some forms of human cancer, is plausible and deserves additional study.
REFERENCES
(1) Berwick M, Armstrong BK, Ben-Porat L, Fine J, Kricker A, Eberle C, et al. Sun exposure and mortality from melanoma. J Natl Cancer Inst 2005;97:195–9.
(2) Smedby KE, Hjalgrim H, Melbye M, Torrang A, Rostgaard K, Munksgaard L, et al. Ultraviolet radiation exposure and risk of malignant lymphomas. J Natl Cancer Inst 2005;97:199–209.
(3) Egan KM, Sosman JA, Blot WJ. Sunlightand reduced risk of cancer: is the real story vitamin D? J Natl Cancer Inst 2005;97:161–3.
(4) Hughes AM, Armstrong BK, Vajdic CM, Turner J, Grulich AE, Fritschi L, et al. Sun exposure may protect against non-Hodgkin lymphoma: a case-control study. Int J Cancer 2004;112:865–71.[CrossRef][Web of Science][Medline]
(5) Jemal A, Devesa SS, Hartge P, Tucker MA. Recent trends in cutaneous melanoma incidence among whites in the United States. J Natl Cancer Inst 2001;93:678–83.
(6) Jemal A, Clegg LX, Ward E, Ries LA, Wu X, Jamison PM, et al. Annual report to the nation on the status of cancer, 1975–2001, with a special feature regarding survival. Cancer 2004;101:3–27.[CrossRef][Web of Science][Medline]
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J Natl Cancer Inst 2005 97: 1158.
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