Research has elucidated how radiation from tanning beds increases the mutation burden across a broad area of melanocytes, thereby significantly raising the risk of developing melanoma. Findings published in Science Advances show that individuals who used tanning beds had a 2.85-fold higher risk of melanoma compared with nonusers, even in typically sun-protected parts of the body.
“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 first study author Pedram Gerami, MD, Professor of Skin Cancer Research at Northwestern University Feinberg School of Medicine. “That has never been shown before.”
“In outdoor sun exposure, maybe 20% of your skin gets the most damage. In tanning bed users, we saw those same dangerous mutations across almost the entire skin surface," Dr. Gerami added.
Background and Study Methods
Use of tanning beds has seen an uptick over the past several years, despite prior suggestions that use could be associated with increased melanoma risk. The incidence of melanoma has also been rising, in part due to increased screening, but as incidence has disproportionately affected young women more recently, tanning beds are increasingly being found responsible.
The World Health Organization has already classified tanning beds as a group 1 human carcinogen, along the lines of asbestos or cigarette smoke, based on previously available research.
Yet the underlying cause of melanomagenesis from tanning bed exposure was previously not understood to explain the increased risks.
Researchers conducted a case/control epidemiological study of the patterns of melanoma in patients with quantifiable tanning bed usage (n = 2,932) compared with nonusers (n = 2,925) age-matched to the case cohort. They then completed molecular analyses of skin cells from a subset of these patients and had tanning bed users answer questions about their history of tanning bed usage to quantify the exposure.
Key Findings
In the epidemiological portion of the study, researchers found that the incidence of melanoma in the tanning bed cohort was 5.1% as compared with 2.1% in the control cohort (odds ratio = 2.85; 95% confidence interval = 2.0–3.99; P < .0001). A dose-response relationship indicated that the relative risk for melanoma increased with the quantity of tanning bed usage (P < .0001).
Tanning bed users also developed melanoma in a different anatomic distribution, with melanomas more commonly found on locations that received lower cumulative sun damage than melanomas in the nonusers group (76.1% vs 61.2%). Multiple primary melanomas were also more common with tanning bed exposure than in nonusers.
Molecular analyses showed that the mutation burden of melanocytes was nearly twofold higher in tanning bed users as in the control groups (median = 5.69 vs 2.86 mutations per megabase [mut/Mb]). By anatomic site, in the upper back, the median mutation burden was 8.82 mut/Mb in tanning bed users vs 4.60 mut/Mb in control groups, and for the lower back, the median mutation burdens were 5.19 mut/Mb and 2.05 mut/Mb, respectively. Robust linear mixed-effects models showed that tanning bed users had a significantly higher mutation burden than nonusers.
Mutational signature analysis found signature 7, which has been associated with ultraviolet radiation–induced damage, to be the dominant signature in cells from all tested subjects (95.1% vs 90.7%), with tanning bed users showing a nonsignificant increase in signature 7 proportions in their cells. A statistically significant increase in SBS11 was found in tanning bed users vs nonusers (14.7% vs 5.5%), with the presence more evenly spread out in the tanning bed users.
Additionally, the researchers found 40 pathogenic mutations present in 23 unique melanocytes, which could be drivers of melanoma. Melanocytes from tanning bed users were more likely to have a pathogenic mutation than those from control subjects (23% vs 7.3%).
Dr. Germani believes that these findings support the need for policy change. “When you buy a pack of cigarettes, it says this may result in lung cancer,” he said. “We should have a similar campaign with tanning bed usage."
“At the very least, indoor tanning should be illegal for minors,” he added.
Disclosure: The study was funded by the 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. For full disclosures of the study authors, visit science.org.
