Non-melanoma skin cancer sunbed risk

Sunbeds are “linked to 100,000 cancer cases a year in the UK”, the Daily Express reports.

The story comes from a major review of studies looking at the association between sunbed use and non-melanoma skin cancers (NMSCs).

Previous studies have already established a link between sunbed use and a much more serious and often fatal type of skin cancer known as malignant melanoma.

This new study found that those who had used sunbeds had a significantly higher risk of developing NMSCs compared with those who had never used them. Three studies suggested a particularly high risk in those who used sunbeds before the age of 25.

NMSCs are slower growing and less aggressive than malignant melanoma, and can usually be cured completely by surgical removal. However, they do place considerable strain on NHS resources as they are both common (an estimated 100,000 cases occur each year in the UK) and expensive to treat.

Because of this some experts are now calling for Europe to follow the example of the US by introducing a ‘tan tax’ on sunbed salons. The hope is that this would discourage people from using indoor tanning facilities and offset some of the costs of treating NMSCs.
 
One expert, quoted by the BMJ, estimated that a tan tax of 10% could raise more than 100 million pounds each year in the UK.

Where did the story come from?

The study was carried out by researchers from Stanford University School of Medicine, University of California and Harvard Medical School, all in the US, and the University of Cambridge. It was funded by the National Institutes of Health.

The study was published in the peer-reviewed British Medical Journal.

The study was covered fairly in the papers, although some of the headlines used were misleading. The Daily Express claim that sunbed use is linked to all 100,000 cases of NMSCs that develop annually in the UK is misleading. NMSCs can have a wide range of causes, including exposure to natural sunlight and family history.

The researchers estimate that in the US, sunbeds account for 3.7% of all cases of basal cell carcinoma and 8.2% of squamous cell cancer. If a similar pattern exists here in the UK then sunbed use is actually responsible for 11,900 cases of NMSCs (which is still unacceptably high for a preventable condition).

The Daily Telegraph leads with the somewhat baffling headline ‘Skin cancer: sun beds cause 1 in 20 cases of malignant melanoma’. This study, in fact, specifically looked at non-melanoma types of skin cancer. The confusion could have arisen from an accompanying editorial in the BMJ, which does discuss the findings of several studies into both melanoma and non-melanoma.

What kind of research was this?

This was a systematic review and meta-analysis that looked at the association between indoor tanning and non-melanoma skin cancer (NMSC). The review has combined observational studies looking at the effect of exposure to sunbeds on the outcome of non-melanoma skin cancer (NMSC).

NMSCs include squamous cell carcinoma and basal cell carcinoma. These types of skin cancer are slower growing and less aggressive than malignant melanoma, and can usually be cured completely by surgical removal. Like melanoma, these types of skin cancer are well known to be caused by exposure to ultraviolet (UV) light.

The researchers point out that cases of the NMSCs basal cell and squamous cell carcinoma have increased dramatically over past decades, particularly in women and younger people, with exposure to the sun’s ultraviolet rays known to be a major risk factor. They say that NMSCs, although less aggressive than malignant melanoma and not usually fatal, are by far the most common human malignancy and are a “considerable financial burden” to healthcare systems. Indoor tanning, they say, is significantly associated with an increased risk of malignant melanoma, with some evidence that it also increases the risk for non-melanoma cancers.

What did the research involve?

The researchers carried out their review in accordance with established guidelines. They identified relevant studies on indoor tanning and the risk of NMSCs using a number of electronic databases. They included in the study all articles that reported on the statistical association between indoor tanning and NMSCs or that reported measuring or adjusting for indoor tanning in any study, which included participants with NMSC. Articles that included no data, such as review articles and editorials, and articles in languages other than English, were excluded.

For each study they followed an established template to extract the relevant data. This included characteristics of the study’s participants, inclusion and exclusion criteria, study design, outcomes and statistical methods used. They used standard statistical techniques to analyse the association between “ever using” a sunbed and the risk of NMSC. They carried out additional analyses on studies that looked at the effects of regular indoor tanning (defined differently by different studies) and on studies that reported on the effects of sunbed use at a young age.

What were the basic results?

The researchers included 12 studies covering 9,328 cases of non-melanoma skin cancer (7,645 basal cell carcinomas and 1,683 squamous cell).

The pooled results of the studies found that, compared with people who never used a sunbed, those who reported “ever using” indoor tanning had:

• a 67% higher risk of developing squamous cell carcinoma (relative risk 1.67, 95% confidence interval (CI) 1.29 to 2.17) and
• a 29% higher risk of developing basal cell carcinoma (relative risk 1.29, 95% CI 1.08 to 1.53)

On the basis of data from three studies, there was a suggestion that indoor tanning before the age of 25 was more strongly associated with NMSCs. However, the increased risk was only significant for basal cell carcinoma. There was a 40% significant increase in risk of basal cell for those using sunbeds before the age of 25 (95% CI 1.29 to 1.52), and a non-significant doubled risk of squamous cell carcinoma (95% CI 0.70 to 5.86).

From their findings, the researchers estimate that, in the US, indoor tanning accounts for 8.2% of all cases of squamous cell carcinoma and 3.7% of all cases of basal cell carcinoma.

This corresponds to 170,652 cases of NMSCs each year estimated to be attributable to indoor tanning. As mentioned, if a similar pattern existed in the UK, indoor tanning would be responsible for an estimated 11,900 cases per year in the UK.

The researchers say that “no significant heterogeneity” existed between studies. This means the studies all had broadly similar findings. This is important as it increases the reliability of the combined results. They also say that further analysis of the data did not substantially affect the findings.

How did the researchers interpret the results?

The researchers say that indoor tanning is associated with a significantly increased risk of both basal and squamous cell skin cancer and the risk is higher with use of sunbeds in early life.

They point out that sunbed use may account for hundreds of thousands of cases of non-melanoma skin cancer each year in the US alone and many more worldwide.

“These findings contribute to the growing body of evidence on the harms of indoor tanning and support public health campaigns and regulation to reduce exposure to this carcinogen,” they argue.

Conclusion

This is a well conducted systematic review that provides evidence that indoor tanning is associated with increased risk of the non-melanoma skin cancers, basal cell and squamous cell carcinoma. As UV light exposure is already known to be the strongest risk factor for these cancers, as well as the more aggressive malignant melanoma, this finding is hardly surprising.

As the researchers point out, their review only included observational studies and so cannot prove that sunbed use caused the development of non-melanoma skin cancers.

Observational studies (as opposed to randomised controlled trials) may be affected by other factors, called confounders, which affect the reliability of the results.

For example, people who use sunbeds might have other lifestyle factors that increase their risk of skin cancers. They may sunbathe outside more often, for instance, or be less likely to use sunscreen. Also, fair-skinned people who are more susceptible to NMSCs might use indoor tanning more.

Although the best studies try to account for such factors, it is always possible that they will affect the results.

That said, the findings on sunbeds and NMSCs are consistent with previous studies and add to the growing body of evidence on the harms of indoor tanning, which is already considered a class 1 carcinogen on the basis of its association with malignant melanoma.

It is well established that both melanoma and non-melanoma skin cancers are associated with exposure to UV rays, so a higher risk associated with sunbeds is entirely plausible. This study will no doubt be given consideration by policymakers concerned about the dangers of sunbeds.

In a related editorial a public health expert argues that the EU should adopt a ‘tan tax’ similar to that introduced by the US government in 2010, where an extra 10% is added to the cost of using indoor tanning, which is then given to the government. The expert argues that this would both:

• discourage people from using indoor tanning, and
• make people who are exposing themselves to preventable risk factors for disease pay for some of the health costs that the disease incurs (in the same way alcohol and tobacco are taxed)