A new meta-analysis offers compelling evidence on the causal relationship between indoor tanning and skin cancer risk.
About 5% to 8% of all melanoma and non-melanoma skin cancers diagnosed in Canada in 2015-or approximately 5,000 cases-are attributable to indoor tanning bed use, according to a recent study published in Cancer Epidemiology.
“There is copious evidence that being a user of indoor tanning increases your risk of skin cancer, and studies like this put that increased risk into a public health context,” said Mackenzie Wehner, MD, MPhil, clinical instructor and post-doctoral research fellow in dermatology at the University of Pennsylvania, in an interview with Cancer Network. “In other words, this study addressed how many skin cancers we might be able to prevent if no one used indoor tanning.”
Lifetime use of an indoor tanning device was associated with relative risks of 1.38 for melanoma (95% CI, 1.22–1.58), 1.39 for basal cell carcinoma (BCC; 95% CI, 1.10–1.76), and 1.49 for squamous cell carcinoma (SCC; 95% CI, 1.23–1.80). Of 5,000 total skin cancer cases in Canada in 2015, a total of 7.0% of melanomas, 5.2% of BCCs, and 7.5% of SCCs were caused by ever-use of indoor tanning devices. Of note, the population attributable risk was higher in women than in men and decreased with increasing age.
The researchers estimated the relative risks for skin cancer subtypes by conducting meta-analyses; they also estimated the prevalence of indoor tanning using the 2006 National Sun Survey. Age- and sex-specific melanoma data for 2015 were obtained from the Canadian Cancer Registry. Incidence data for non-melanoma skin cancer was gathered from the 2015 Canadian Cancer Statistics report. The researchers also accounted for ethnicity, which, according to Wehner, “is a more nuanced and conservative way to do the calculations than previous studies have used.”
Wehner drew comparisons between the current study and similar studies. “This study reports smaller, though still sizeable, percentages of skin cancers that are attributable to, or caused by, indoor tanning. This is likely because the authors did a more detailed analysis than has previously been done – they included age, gender, and ethnicity in their estimates,” she said. “Additionally, this study is specific to Canada.”
However, it may have limitations, said Wehner. “Notably, the authors estimated the number of people who had ever used indoor tanning by converting the number who had used indoor tanning in the past year. This is from published data, but it may not be valid,” she said. “Additionally, Canada does not have a registry for two of the skin cancer types (neither does the US), and this likely led to an underestimate of the number of skin cancers attributable to indoor tanning.”
In a separate interview with Cancer Network, Jerry D. Brewer, MD, MS, a professor of dermatology at the Mayo Clinic in Rochester, Minnesota, stressed the definitiveness of the study. “Tanning beds are known to cause cancer, and not just the common forms of skin cancer-basal and squamous cell carcinoma-but melanoma as well,” he said. “The evidence is now overwhelming.”