By Anthony J. Brown, MD
NEW YORK (Reuters Health) - Two new studies suggest that exposure to sunlight might not be as risky for cancer as is generally believed.
Scandinavian researchers show that high UV radiation exposure is associated with a reduced risk of lymphoma, while another team reports that sunlight-related melanoma skin cancers appear to be inherently less aggressive than those that arise in non-exposed areas.
Dr. Karin Elkstrom Smedby, from the Karolinska Institute in Stockholm, and colleagues investigated ultraviolet radiation exposure as a possible cause for the increasing rates of malignant lymphoma seen in recent decades.
Instead, the researchers found that high UV radiation exposure, as measured by frequent sunbathing and sunburns, cut the risk of the non-Hogkins type of lymphoma by up to 40 percent depending on the level of exposure.
The study involved 3740 patients with malignant lymphomas who were compared with 3187 matched "controls" from the general population. High UV radiation exposure also seemed to protect again the Hodgkin's type of lymphoma, but the association was weaker than with non-Hodgkin's disease.
In another study, also reported in the Journal of the National Cancer Institute, researchers note that sun exposure has been linked to better survival in patients with melanoma. The new research suggests that this is due, at least in part, to sunlight-related tumors being inherently less aggressive than those not tied to sun exposure.
"Our findings provide the strongest evidence to date that the better prognosis of (sunlight-related) melanomas is not simply due to earlier detection of these types," Dr. Marianne Berwick told Reuters Health.
Berwick, a researcher from the University of New Mexico in Albuquerque, noted that "further studies are needed to determine how sun exposure might reduce melanoma aggressiveness," but said that it could have something to do with increased production of vitamin D, or involve an enhanced ability of cells to repair DNA damage.
The findings stem from a study of 528 melanoma patients who were entered in the Connecticut Tumor Registry.
Sunburn, high intermittent sun exposure, self-reported skin awareness, and solar elastosis -- a marker of sun damaged-skin -- were all linked to increased survival from melanoma.
Upon analysis, skin awareness was a strong predictor of better survival, consistent with the belief that earlier detection leads to better outcomes. However, solar elastosis, which does not relate to detection, was found to be an even stronger predictor of increased survival.
Berwick emphasized that these findings have no bearing on current recommendations that "avoiding sun exposure reduces the risk of melanoma." Moreover, she added that they also do not suggest that exposing melanomas to sunlight after they've developed will improve survival.
SOURCE: Journal of the National Cancer Institute, February 2, 2005.