Study is first to show how tanning beds mutate skin cells far more than ordinary sunlight
Melanoma, the deadliest skin cancer, kills about 11,000 in
the U.S. each year. Despite decades of warnings, the precise biological
mechanism behind tanning beds’ cancer risk remained unclear. The indoor tanning
industry, which is
making a comeback, has used that uncertainty to argue that tanning beds are
no more harmful than sunlight.
This new study “irrefutably” challenges those claims by
showing how tanning beds, at a molecular level, 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, professor of skin cancer research at Northwestern University
Feinberg School of Medicine. “That has never been shown before.”
The study was published in Science Advances.
A clinical mystery
Gerami, who also directs the melanoma program in dermatology
at Northwestern, has been treating melanoma patients for 20 years. Over the
years, he noticed an unusually high number of women under 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 (the
pigment-producing skin cells where melanoma begins) from three skin donor
groups.
The first group included 11 patients from Gerami 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% of your skin gets the
most damage,” Gerami said. “In tanning bed users, we saw those same dangerous
mutations across almost the entire skin surface.”
Melanoma survivor donates skin biopsy
The study would not have been possible without the
generosity of Gerami’s patients who donated their biopsies. One of them,
49-year-old Heidi Tarr from the Chicago area, used tanning beds heavily during
high school — two to three sessions a week — because friends and celebrities at
the time were also doing it and “it felt like that's what made you beautiful.”
Decades later, as a mother in her thirties, she noticed a
mole on her back and immediately feared the worst. Her melanoma diagnosis led
to surgery, years of frequent follow-up visits and more than 15 additional
biopsies as new moles appeared. “The biopsies can be painful, but the mental
anxiety is worse,” she said. “You’re always waiting for the call that it’s
melanoma again.”
When Gerami explained the study, she volunteered more
biopsies without hesitation. “I value science, and I wanted to help,” she said.
“If what happened to my skin can help others understand the real risks of
tanning beds, then it matters.”
‘Wronged by the industry’
After seeing the biological and clinical evidence side by
side, Gerami said the need for policy change is clear. “At the very least,
indoor tanning should be illegal for minors,” he said.
“Most of my patients started tanning when they were young,
vulnerable and didn’t have the same level of knowledge and education they have
as adults,” he said. “They feel wronged by the industry and regret the mistakes
of their youth.”
Gerami also said tanning beds should carry warnings similar
to those on cigarettes. “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. The World Health Organization has deemed tanning beds to be
the same level of carcinogen as smoking and asbestos. It’s a class one
carcinogen.”
Gerami suggests that anyone who frequently tanned earlier in
life should have a total-body skin exam by a dermatologist and be evaluated for
whether they need routine skin checks.
Gerami is a member of the Robert H. Lurie Comprehensive
Cancer Center of Northwestern University.
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.
