Opponents square off in online debate over whether sun exposure causes melanoma

London - The issue of whether sun exposure is a major cause of melanoma is the subject of two opposing articles published July 22 on bmj.com, the Web site of the British Medical Journal, HealthDay News reports.

In his article, Dr. Scott W. Menzies, Ph.D., of the University of Sydney, writes that sun exposure is a cause of melanoma because the site patterns of melanoma are the same as those of sun exposure, and because melanoma incidence is higher among races that tend to be easily susceptible to sunburn.

Writing in his opposing article, Sam Shuster, of Norfolk and Norwich University Hospital in Norwich, England, argues that linking melanoma with sun exposure is a case of descriptive epidemiology in which association is confused with cause. The variation in melanoma incidence is more ethnic than pigmentary, he writes, noting that 75 percent of melanomas are found on unexposed sites. Additionally, he writes, the sun-exposure theory is weakened by the lack of impact on incidence by use of sun beds and inconsistent evidence on the effect of sunscreens.

“Melanomas are difficult to produce experimentally with ultraviolet light and are far less common than non-melanoma cancers in xeroderma pigmentosum,” Shuster argues in his article. “Therefore, the effect of ultraviolet light can only be minimal, and the case against a major role is clear. Attempts to relate light exposure to surface area and site are irrelevant, since the cell of origin of melanoma and its distribution are unknown.”