Indoor sunbathing exposes normal skin to mutations linked to melanoma.

Indoor sunbathing exposes normal skin to mutations linked to melanoma.

By linking tanning bed use to widespread genetic damage in healthy skin cells, this study shows how artificial UV exposure can prime skin for melanoma long before tumors appear.

In a recent study published in the journal Science Advances was published, researchers provided high-resolution molecular evidence of the link between indoor sunbathing and an increased risk of melanoma. The study compared single-cell resolution genomic data from clonally expanded melanocytes from individuals with very high lifetime tanning bed use versus a control group and found that the former group had a significantly higher number of DNA mutations compared to non-users.

Crucially, these mutations were common in melanocytes, the pigment-producing cells that occur in areas of the body that are normally protected from natural sunlight, such as the lower back. The study also identified a specific cluster of disease-causing, cancer-promoting mutations in externally normal-looking skin. These results challenge industry claims about the safety of artificial UV radiation and offer a biological mechanism that may help explain why tanning bed users often experience multiple sunburns at younger ages Melanoma develop.

Burden of melanoma and debate about UV exposure

Melanoma is the medical term for tumors, particularly malignant tumors, of melanin-producing cells that are typically associated with skin cancer. Worldwide, melanoma is one of the deadliest forms of skin cancer, with public health reports finding that it is responsible for approximately 11,000 deaths annually in the United States alone.

While decades of research have established the primary origin of these cancers as exposure to UV radiation, the debate over artificial sources of UV remains contentious. While scientists and clinicians believe that artificial tanning beds can increase the risk of skin cancer, their manufacturers and marketers emphasize their safety. As a result, despite the World Health Organization's (WHO) classification of tanning beds as Group 1 carcinogens, nearly 30 million Americans reportedly use them each year.

Tanning bed industry claims and contradictions

The tanning bed industry often promotes indoor sunbathing devices as controlled, safer alternatives to natural sunlight, arguing that these devices emit a higher ratio of ultraviolet A (UVA) to ultraviolet B (UVB) light, which supposedly reduces the risk of sunburn-induced melanoma. Additionally, it is often suggested that a pre-vacation bag protects the skin from future damage.

However, recent clinical data suggests that young women who use tanning beds often develop melanomas on the trunk and buttocks, areas typically exposed to low levels of sunlight in the general population. To date, the specific cellular and molecular mechanisms driving these observations remain unclear.

Study structure and data sources

The present study aims to address this ongoing debate and inform future public health recommendations by analyzing the DNA of skin cells to better understand how artificial UV radiation may contribute to the development of melanoma. The study consisted of two main components: a large-scale epidemiological analysis and high-resolution genomic sequencing of melanocytes.

Epidemiologic data were obtained from Northwestern Medicine Department of Dermatology patient records (n = 32,315) obtained from a high-risk population in a dermatology clinic. These records were categorized into a case group of 2,932 patients with quantifiable history of tanning bed use and an age-matched control group of 2,925 non-users. This design allowed researchers to map the anatomical distribution of melanomas in different parts of the body and estimate the adjusted odds of melanoma associated with indoor sunbathing.

Methods of genomic sequencing of melanocytes

Genetic sequencing data were collected by taking biopsies of normal, non-tumorous tissue from the upper and lower backs of 11 heavy tanning bed users, defined as individuals with more than 50 sessions over their lifetime, with reported exposure ranging from dozens to several hundred sessions. These samples were compared to two control groups: patients from a high-risk skin cancer clinic and cadaver donors from the general population who had no tanning bed exposure histories.

Melanocytes were isolated from these biopsies, clonally expanded in culture, and subjected to whole-exome single-cell resolution and transcriptome sequencing to provide detailed comparisons of the Mutation burden and mutagenic signatures via individual pigment-producing cells.

Epidemiological and molecular results

The analyzes provide strong evidence of the harmful effects of artificial UV exposure. Epidemiologically, the likelihood of developing melanoma on areas of the body that typically receive little cumulative sun exposure, such as the trunk, was significantly higher in tanning bed users than non-users (76.1% vs. 61.2%).

After adjusting for age and family history, tanning bed users were 2.85 times more likely to develop melanoma than controls. The analysis also found a higher likelihood of multiple primary melanomas in people with a history of tanning bed use.

Genetic sequencing showed striking differences between cases and controls. Melanocytes from tanning bed users had a higher overall mutation burden, with a median of 5.69 mutations per megabase of DNA compared to 2.86 mutations per megabase in controls. Importantly, this increased mutation load was even observed in biopsies from the lower back, confirming that tanning beds can damage skin in areas that are normally protected from natural sunlight. The study also found that melanocytes from the upper back, which may be exposed, also had high mutation loads in both groups.

While the classic UV-associated mutational damage signature SBS7 was predominant in all samples, melanocytes from tanning bed users showed a significantly higher relative contribution of the mutational signature SBS11. The biological origin of this signature remains uncertain, and the authors caution that its interpretation requires further validation, but its enrichment in tanning bed users suggests potential differences in the mutagenic effects of artificial UV exposure.

Notably, melanocytes from tanning bed users were significantly more likely to carry disease-causing, cancer-promoting mutations, despite appearing histologically normal. These mutations were detected in the sampled sites, with a higher proportion found in upper back melanocytes than in those of the lower back, indicating a widespread field of genetically altered cells rather than isolated areas of damage, and suggesting a potential mechanism for the development of multiple primary melanomas.

Public health implications and prevention

The study establishes a robust molecular and epidemiological association between indoor sunbathing and melanoma, particularly in individuals with intensive lifetime use. Rather than providing a safe alternative to natural sunlight, artificial sunbathing appears to increase the risk of melanoma by increasing the mutation burden and expanding the number of melanocytes carrying disease-causing mutations throughout the skin.

These findings undermine the tanning industry's narrative about safe tanning and suggest that practices like pre-holiday tanning may instead be burdening normal skin with genetic changes that increase susceptibility to melanoma, especially at younger ages.

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