A Solar Paradox?

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Summary and Comment

A Solar Paradox?

Researchers present a surprising relation between sunburn and melanoma survival.

Decades of epidemiologic data have established the relation between excessive sun exposure and melanoma risk. These results form the basis of our current melanoma-prevention strategies, namely, sun protection. However, the role of sun exposure in melanoma mortality has not been well studied. One fundamental supposition is that solar exposure modulates the initial risk for developing melanoma but not the risk for metastasis once the tumor has formed.

In a population-based, case-control study of melanoma in Connecticut, 528 patients were followed over 15 years. During this period, 58 (11%) died of melanoma. Univariate analysis showed that patients with histories of severe sunburn or intermittently high levels of sun exposure were significantly less likely to die (hazard ratios, 0.5 and 0.6, respectively) than those who had never been sunburned and those with low exposure. Solar elastosis (a histologic indicator of cutaneous sun damage) was also inversely associated with melanoma mortality (HR, 0.5). Interestingly, skin awareness (positive answers to "Did you ever think about your skin, how it looked, whether there were any changes, or whether there were any abnormal marks?"), but not self- or physician examination, was also associated with decreased mortality. In multivariate analysis, solar elastosis and skin awareness, but not history of sun exposure, remained predictors of survival. Other known predictors, such as thicker tumors and ulceration, were also validated in this study.

Comment: This intriguing study suggests that severe, intermittent sun exposure somehow protects against death, even though the risk for developing melanoma increases with exposure. It is difficult to understand how intense sun exposure before melanoma formation can modulate survival after tumor development. Sunscreen was not considered; the data were gathered in the 1980s, when few consistently used it. Melanoma incidence has risen out of proportion to mortality over the past decades; some have postulated that sun exposure may contribute to the formation of less aggressive melanomas. In this paradigm, the faster-growing, lethal melanomas may have less relation to sun exposure. The authors also considered vitamin D and enhanced melanization as protective mechanisms, and solar elastosis may produce an antimetastatic shield. These possibilities remain hypothetical until more studies are performed.

— Hensin Tsao, MD, PhD

Published in Journal Watch Dermatology March 2, 2005