Study clarifies elevated melanoma risk from indoor tanning

Tanning bed use is tied to almost a threefold increase in melanoma risk, and findings from new research show these devices cause melanoma-linked DNA damage across nearly the entire skin surface.

The findings were reported in a study published in Science Advances led by Northwestern Medicine in Chicago and the University of California, San Francisco.

This new study “irrefutably” challenges claims from the tanning industry that tanning beds are no more harmful than sunlight by showing how the devices mutate skin cells far beyond the reach of ordinary sunlight, according to the authors.

“Even in normal skin from indoor tanning patients, areas where there are no moles, we found DNA changes that are precursor mutations that predispose to melanoma,” said study first author Dr. Pedram Gerami, in a press release. “That has never been shown before.”

Dr. Gerami is a professor of skin cancer research at Northwestern University Feinberg School of Medicine.

A clinical mystery

Dr. Gerami, who also directs the melanoma program in the department of dermatology at Northwestern, has been treating melanoma patients for 20 years. Over the years, he noticed an unusually high number of women under age 50 with a history of multiple melanomas, and suspected the linking factor was tanning bed usage. So, along with his research team, he designed the epidemiologic part of the study and compared the medical records of roughly 3,000 tanning bed users with 3,000 age-matched controls with no history of indoor tanning.

The team found that melanoma was diagnosed in 5.1% of tanning bed users compared with 2.1% of non-users. After adjusting for age, sex, sunburn history and family history, tanning bed use remained associated with a 2.85-fold increase in melanoma risk.

Tanning bed users were also more likely to develop melanoma on sun-shielded body sites, such as the lower back and buttocks. These findings supported the idea that tanning beds may cause broader DNA injury than sun exposure.

DNA sequencing

To test that hypothesis, the scientists used new genomic technologies to perform single-cell DNA sequencing on melanocytes from three skin donor groups.

The first group included 11 of Dr. Gerami’s patients with long histories of indoor tanning. The second group consisted of nine patients who had never used tanning beds but were otherwise matched for age, sex, and cancer risk profiles. A third group of six cadaver donors supplied additional skin tissue to round out the control samples.

The scientists sequenced 182 individual melanocytes and found skin cells from tanning bed users carried nearly twice as many mutations as those from controls and were more likely to contain melanoma-linked mutations. In indoor tanners, the mutations also appeared in body areas that typically remain protected from the sun, confirming that tanning beds create a broader field of DNA injury.

“In outdoor sun exposure, maybe 20 per cent of your skin gets the most damage,” Dr. Gerami said. “In tanning bed users, we saw those same dangerous mutations across almost the entire skin surface.”

The study was funded by the U.S. National Institutes of Health, the Department of Defense Melanoma Research Program, the Melanoma Research Alliance Team Science Award, the Melanoma Research Alliance Dermatology Fellows Award, the LEO Foundation Region Americas Award, Cancer Center Support, the IDP Foundation Award and the Greg and Anna Brown Family Foundation Award.