In the past year, the evidence linking ultraviolet (UV) tanning to melanoma, the deadliest skin cancer, has grown considerably stronger. In July 2009, the International Agency for Research on Cancer (IARC), affiliated with the World Health Organization (WHO), announced that UV radiation from tanning machines had been added to its infamous Group I — substances such as plutonium deemed “carcinogenic [cancer-causing] to humans.” The IARC’s special report in The Lancet marked its official recognition that tanning devices are a comparable cause of cancer.
Although it has long been generally acknowledged that about 90 percent of nonmelanoma skin cancers (NMSC), such as basal and squamous cell carcinoma, are associated with exposure to UV radiation, UV’s link to melanoma has been debated. But in their report, members of the IARC’s Monograph Working Group cited comprehensive studies showing that risk of melanoma increased by 75 percent when tanning bed use began before age 35.
The Genetics of a Melanoma
Despite the IARC report, some experts remained skeptical. Heredity plays a significant role — a family history of melanoma greatly increases the risk of developing the disease — and some scientists argued there was still no convincing proof of a link between UV radiation and melanoma. Then, in December, 2009, scientists revealed the strongest evidence yet that some melanomas are caused by exposure to UV radiation.
When researchers at The Wellcome Trust Sanger Institute, in Hinxton, UK, mapped the complete genetic material (the genome) that composed a melanoma taken from a patient with the disease, they identified thousands of mutations. Mutations are changes or errors in genes caused by radiation, viruses, and other causes, and some can ultimately lead to cancer. According to the Sanger Institute,
“The melanoma genome contains more than 33,000 mutations, many of which bear the imprint of the most common cause of melanoma — exposure to ultraviolet light.”
The scientists compared the genomes of both normal and melanoma tissue to pinpoint where in the melanoma the mutations occurred, and saw exactly how UV exposure had affected DNA.
“We can see the desperate attempts of our genome to defend itself against the damage from ultraviolet radiation,” the study’s coauthor, Mike Stratton, MD, PhD, explained. “Our cells fight back furiously to repair the damage, but frequently lose that fight.” The result can be melanoma.
It’s not clear yet to just what extent UV radiation influences the development of melanoma, but this research, published in Nature, all but confirms UV radiation as a cause of melanoma.