Indoor More Risky Than Outdoor Tanning for Melanoma?

Kate Johnson

March 19, 2012

March 19, 2012 (San Diego, California) — Indoor tanning might be a more reliable predictor of invasive cutaneous melanoma than outdoor sunburns, according to a study presented here at the American Academy of Dermatology 70th Annual Meeting.

The findings build on the results of the Minnesota Skin Health Study, which found an increased risk for melanoma (odds ratio, 1.74) with ever tanning indoors (Cancer Epidemiol Biomarkers Prev. 2010;19:1557-1568), but did not directly compare the risk of outdoor and indoor ultraviolet (UV) exposure.

The new analysis, which involved 1167 cases diagnosed from 2004 to 2007 and 1101 control subjects, combined personal and environmental factors to predict a patient's risk of developing melanoma.

Although there are other models, "none are population-based, which limits generalizability...and none include indoor tanning exposure," said Lauren Smith, MD, from New York University Langone Medical Center in New York City.

The development of a reliable model that could be used in clinical practice would allow physicians to combine patient self-reported history with clinical information to estimate overall melanoma risk, and would facilitate the development of management recommendations based on individual risk, she explained.

In the Minnesota Skin Health Study, patients diagnosed with melanoma were 60% female, had a mean age of 45.6 years, and were age- and sex-matched with control subjects who were randomly selected from state driver's license lists.

The study used self-administered questionnaires and telephone interviews to collect information on personal risk factors such as family history and phenotypic factors (eye, skin, and hair color, moles and freckling). They also asked about the use of indoor tanning, the types of devices used, initiation age, period of use, dose, duration, indoor-tanning-related burns, and outdoor UV exposure.

"Outdoor sun exposure means different things to different people," DeAnn Lazovich, PhD, from the University of Minnesota, Minneapolis, and senior investigator on the study, told Medscape Medical News. "In this study, it is measured by lifetime sunburns, which represents intense intermittent exposure...even if the person had very little regular outdoor exposure."

The study found that 4 UV risk factors were significantly associated with melanoma: outdoor lifetime sunburns, indoor tanning, frequency of indoor tanning, and burns from indoor tanning (P < .0001 for all).

However, when these factors were combined with personal risk factors (age, sex, family history, and phenotypic factors), outdoor lifetime sunburns became much less significant (P = .8) than indoor tanning frequency (P = .026).

An initial model, using only personal factors (age, sex, family history, and phenotypic factors) gave an area-under-the-curve (AUC) predictability of 72%, meaning that "if we evaluated 100 patients, this model would adequately predict the risk of 72 of those patients," said Dr. Smith.

Adding outdoor lifetime sunburns to the model increased this predictability to 73%, "but with a P value of .8, this wasn't significant, meaning that the addition of outdoor burns did not improve the predictability of the first model," she explained.

"We then took out outdoor burns and added indoor UV exposure (ever/never indoor tanning, frequency of use, and burns), that increased our AUC to 74%, which was statistically significant [P = .026], meaning that the addition of indoor UV exposure did significantly improve the risk model."

Although the Minnesota Skin Health Study was the first to establish a dose–response relation between indoor tanning and melanoma, it has not discouraged the trend, said Dr. Smith.

"There's a striking average of 42 tanning salons per city, which is more than either Starbucks or McDonald's, so access is definitely a problem," she noted.

Asked to elaborate on the findings, Dr. Lazovich explained that "we have never come up with a good explanation for why sun exposure is not more strongly associated with melanoma risk in our study."

Because phenotype is genetically determined, UV exposure from sun or indoor tanning should theoretically pose the same risk, she said. Indeed, the group's original findings in the Minnesota Skin Health Study found an odds ratio for indoor tanning of 1.74, which is similar to what other metaanalyses have reported for outdoor sun exposure.

"Whether the UV comes from sun or artificial devices, I think that it likely increases the risk of melanoma in the same range of magnitude — it's just that we did not find that in our report."

Another senior investigator on the study, David Polsky, MD, PhD, also from New York University, added that "one difference between outdoor and indoor UV exposure is the wavelengths to which the person is exposed. Indoor tanning uses primarily UVA, and outdoor exposure has both UVA and UVB. Both wavelengths are likely to contribute to melanoma," he told Medscape Medical News. "UVB is what gives you a sunburn outdoors, and since sunburns are a melanoma risk factor, a lot of attention focused on UVB historically. The potential importance of UVA has gained attention over the past few decades, and has led to the addition of UVA filters to sunscreens."

Dr. Lazovich explained that the study found even stronger associations between indoor tanning and melanoma with devices that emit higher amounts of UVB than the sun and those that emit almost exclusively UVA, although these results were based on small numbers.

She said one possible explanation for the lack of association found with outdoor burns is that subjects were generally younger than in other studies, so perhaps the full effect of sun exposure has not yet been fully realized. "Another possibility is that we measured sun exposure poorly, so it's a result of measurement error. We did find indoor tanning exposure to be inversely correlated with sun exposure, so perhaps individuals in Minnesota are substituting indoor for outdoor tanning, which makes some sense, given the Minnesota weather."

That explanation resonates with Richard L. Gallo, MD, PhD, professor and chief of dermatology at the University of California at San Diego, who moderated the session in which the study was presented. He said a common misconception among patients is that indoor tanning before sun exposure protects the skin.

"People often go to tanning salons before they go on vacation," he told Medscape Medical News. "It may be true that you're less likely to burn if you've damaged your skin first by tanning, but we need data to support or refute [the effect on melanoma risk]. This study suggests that indoor exposure is not protective, but the tanning industry is constantly saying these are nonburning rays, this is not UVB as much as UVA, this is safer. The data from their study, although they are early and very preliminary, tend to refute that."

Dr. Smith, Dr. Lazovich, and Dr. Polsky have disclosed no relevant financial relationships. Dr. Gallo reports receiving consulting fees from Allergan and Novartis; investigator grants from Colgate-Palmolive, Galderma Laboratories, L.P., Intendis, and Johnson & Johnson Consumer Products, L'Oreal USA; and being a founder and stockholder of Skin Epibiotics.

American Academy of Dermatology (AAD) 70th Annual Meeting: Late-breaking abstract. Presented March 16, 2012.

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