Each year, an estimated 54,000 people in the United States are diagnosed with melanoma , a potentially deadly form of skin cancer . Over the past 50 years, the incidence of melanoma has significantly increased. At the same time, people have been spending more and more time in the sun. Sun exposure is considered a major risk factor for the development of melanoma, which has lead public health officials to recommend that people avoid excessive sun exposure.
But surprisingly, there is evidence of a possible link between sun exposure and an increased chance of survival from melanoma. How could this be? Some researchers believe that sun exposure may cause some biologic effect that reduces the aggressiveness of melanoma. Others postulate that people who get more sun exposure may just be more aware of their skin cancer risk, leading to earlier detection and better treatment.
A new study in the February 2, 2005 issue of the Journal of the National Cancer Institute looked at markers of sun exposure in more than 500 people who had recently been diagnosed with melanoma. The researchers found that solar elastosis, or sun damage to the skin, was independently associated with increased survival from melanoma.
This study included 528 people from the Connecticut Tumor Registry who were diagnosed with early-stage melanoma (i.e., the cancer had not spread to lymph nodes or organs) between 1987 and 1989. The participants entered this study approximately three months after they were diagnosed with melanoma.
The researchers interviewed the participants in person and collected information on factors that could possibly influence the chances of survival from melanoma, including:
In addition, a pathologist examined a sample of each participant’s skin to determine whether solar elastosis was present and to record features of the melanoma lesion.
The researchers followed the participants for an average of 5.4 years and kept track of deaths that occurred from melanoma.
By the end of the study, 58 (11%) of the participants had died of their melanoma.
Interestingly, sunscreen use within the last 10 years or during childhood was not associated with the risk from melanoma. And all measures of sun exposure (i.e., history of severe sunburn, high levels of intermittent sun exposure, solar elastosis) were associated with a decreased risk of death from melanoma. Furthermore, participants who reported high skin awareness, but not those who reported skin examinations, were at significantly lower risk of death from melanoma.
After adjusting for all the variables that might be associated with melanoma death, history of sunburn and level of intermittent sun exposure were no longer significantly associated with lower risk of death from melanoma, but solar elastosis and skin awareness still were.
While these findings are interesting, they are limited by the fact that the study was based in part on participants’ answers to questions about their behaviors, sometimes in the distant past, which may not be perfectly accurate.
These surprising results suggest that pathological evidence of increased sun exposure reduced the risk of death in patients with early-stage melanoma.
These findings become even more compelling when paired with those of another study in the same issue of the Journal of the National Cancer Institute . The second study, which took place in Denmark and Sweden, compared 3,700 people with malignant lymphomas to 3,200 people without cancer. They found that high frequencies of sunbathing and sunburns before age 21 were associated with a significant 30% to 40% reduction in the risk of developing non-Hodgkin’s lymphoma , the most common type of lymphoma.
What do these seemingly paradoxical results mean? How can excessive sun exposure, which is widely believed to cause cancer, possibly decrease the risk of developing cancer or dying from it? For now, the most plausible explanation is that since sun exposure triggers our bodies to synthesize vitamin D, it may be the vitamin D that works as an anti-cancer agent. This hypothesis is supported by the observation that death rates from some other cancers— breast , prostate , and colon —are higher in people who live in northern states than those who live in southern states.
But don’t throw out the sunscreen and head south just yet. It is important to emphasize that both of these studies are far from conclusive. Much more research is necessary before these findings should influence the public’s behavior on the beach. For now, the best way to prevent skin cancer is to avoid getting too much sun. And, as this study supports, it is important to be aware of your skin and promptly report any changes or abnormal growths to your physician.
American Cancer Society
National Cancer Institute
Berwick M, Armstrong BK, Ben-Porat L, Fine J, Kricker, A, Eberle C, Barnhill R. Sun exposure and mortality from melanoma. Journal of the National Cancer Institute. 2005;97:195–199.
Egan KM, Sosman JA, Blot WJ. Sunlight and reduced risk of cancer: is the real story vitamin D? Journal of the National Cancer Institute. 2005;97:161–163.
Emedby KE, Hjalgrim H, Melbye M, et al. Ultraviolet radiation exposure and risk of malignant melanomas. Journal of the National Cancer Institute. 2005;97:199–209.
Last reviewed Feb 3, 2005 by Richard Glickman-Simon, MD
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