Abstract

Background

'Keratinocyte cancer' is now the preferred term for the most commonly identified skin cancers basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC), which were previously commonly categorised as non‐melanoma skin cancers (NMSC). Keratinocyte cancer (KC) represents about 95% of malignant skin tumours. Lifestyle changes have led to increased exposure to the sun, which has, in turn, led to a significant increase of new cases of KC, with a worldwide annual incidence of between 3% and 8%. The successful use of preventive measures could mean a significant reduction in the resources used by health systems, compared with the high cost of the treatment of these conditions. At present, there is no information about the quality of the evidence for the use of these sun protection strategies with an assessment of their benefits and risks.

Objectives

To assess the effects of sun protection strategies (i.e. sunscreen and barrier methods) for preventing keratinocyte cancer (that is, basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC) of the skin) in the general population.

Search methods

We searched the following databases up to May 2016: the Cochrane Skin Group Specialised Register, CENTRAL, MEDLINE, Embase, and LILACS. We also searched five trial registries and the bibliographies of included studies for further references to relevant trials.

Selection criteria

We included randomised controlled clinical trials (RCTs) of preventive strategies for keratinocyte cancer, such as physical barriers and sunscreens, in the general population (children and adults), which may provide information about benefits and adverse events related to the use of solar protection measures. We did not include trials focused on educational strategies to prevent KC or preventive strategies in high‐risk groups. Our prespecified primary outcomes were BCC or cSCC confirmed clinically or by histopathology at any follow‐up and adverse events.

Data collection and analysis

Two review authors independently selected studies for eligibility using Early Review Organizing Software (EROS). Similarly, two review authors independently used predesigned data collection forms to extract information from the original study reports about the participants, methods of randomisation, blinding, comparisons of interest, number of participants originally randomised by arm, follow‐up losses, and outcomes, and they assessed the risk of bias. We resolved any disagreement by consulting a third author and contacted trial investigators of identified trials to obtain additional information. We used standard methodological procedures expected by Cochrane.

Main results

We included one RCT (factorial design) that randomised 1621 participants.

This study compared the daily application of sunscreen compared with discretionary use of sunscreen, with or without beta‐carotene administration, in the general population. The study was undertaken in Australia; 55.2% of participants had fair skin, and they were monitored for 4.5 years for new cases of BCC or cSCC assessed by histopathology. We found this study to be at low risk of bias for domains such as allocation, blinding, and incomplete outcome data. However, we found multiple unclear risks related to other biases, including an unclear assessment of possible interactions between the effects of the different interventions evaluated (that is, sunscreen and beta‐carotene). We found no difference in terms of the number of participants developing BCC (n = 1621; risk ratio (RR) 1.03, 95% confidence interval (CI) 0.74 to 1.43) or cSCC (n = 1621; RR 0.88, 95% CI 0.50 to 1.54) when comparing daily application of sunscreen with discretionary use, even when analyses were restricted to groups without beta‐carotene supplementation. This evidence was of low quality, which means that there is some certainty that future studies may alter our confidence in this evidence.

We reported adverse events in a narrative way and included skin irritation or contact allergy.

We identified no studies that evaluated other sun protection measures, such as the use of sun‐protective clothing, sunglasses, or hats, or seeking the shade when outdoors.

Authors' conclusions

In this review, we assessed the effect of solar protection in preventing the occurrence of new cases of keratinocyte cancer. We only found one study that was suitable for inclusion. This was a study of sunscreens, so we were unable to assess any other forms of sun protection. The study addressed our prespecified primary outcomes, but not most of our secondary outcomes. We were unable to demonstrate from the available evidence whether sunscreen was effective for the prevention of basal cell carcinoma (BCC) or cutaneous squamous cell carcinoma (cSCC).

Our certainty in the evidence was low because there was a lack of histopathological confirmation of BCC or cSCC in a significant percentage of cases. Amongst other sources of bias, it was not clear whether the study authors had assessed any interaction effects between the sunscreen and beta‐carotene interventions. We think that further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.

Author(s)

Guillermo Sánchez, John Nova, Andrea Esperanza Rodriguez‐Hernandez, Roger David Medina, Carolina Solorzano‐Restrepo, Jenny Gonzalez, Miguel Olmos, Kathie Godfrey, Ingrid Arevalo‐Rodriguez

Abstract

Plain language summary

Sun protection (including sunscreens) to prevent basal cell carcinoma and cutaneous squamous cell carcinoma of the skin

What is the aim of this review?

The aim of this Cochrane Review was to find out if using topical sunscreen and physical barrier methods (such as sun‐protective clothing, hats, sunglasses, and the active search for shade when outdoors) compared with no specific precautionary activity prevented the development of basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (cSCC) of the skin in adults and children.

What was studied in this review?

Keratinocyte cancer (BCC and cSCC of the skin) is the most commonly identified type of skin cancer. The main risk is exposure to ultraviolet radiation, which is a component of sunlight. Prevention has become an important way to manage this cancer, so it is important to assess the effectiveness of methods used to prevent keratinocyte cancer in the general population. In this review, we assessed the effects of using topical sunscreen and physical barrier methods (such as sun‐protective clothing, hats, sunglasses, and the active search for shade when outdoors) compared with no specific precautionary interventions aimed at preventing the development of BCC and cSCC in adults and children.

We searched the medical literature up to May 2016 for randomised controlled trials that evaluated preventive strategies. We found only one study suitable for inclusion. This study compared the daily application of sunscreen (with or without beta‐carotene, which is a precursor of vitamin A) compared with the occasional use of sunscreen (with or without beta‐carotene) in the general population, without restriction by gender or age. The study was undertaken in Australia, where 1621 participants, 55% of them with fair skin, were monitored for 4.5 years for new cases of BCC or cSCC assessed by histopathology (which is a method used to detect cancerous cells under the microscope).

What are the main results of this review?

We found no difference between the number of people who developed BCC or cSCC in the two groups over the time period of the trial. So, there did not seem to be a difference in applying sunscreen daily compared with using it occasionally.

Key messages

Our one included study was a study of sunscreens, so we were unable to assess any other forms of sun protection.

We identified no studies that evaluated other sun protection measures, such as the use of sun‐protective clothing, sunglasses, or hats, or seeking the shade when outdoors.

We did not find evidence for the effectiveness of daily sunscreen for preventing BCC or cSCC compared with the occasional use of sunscreen. The certainty of the evidence was low, which means that future studies may alter this result.

Side effects from the sunscreen used with or without the addition of beta‐carotene included a low percentage of cases of contact allergy and skin irritation.

How up to date is this review?

This review included studies identified up to May 2016.

Author(s)

Guillermo Sánchez, John Nova, Andrea Esperanza Rodriguez‐Hernandez, Roger David Medina, Carolina Solorzano‐Restrepo, Jenny Gonzalez, Miguel Olmos, Kathie Godfrey, Ingrid Arevalo‐Rodriguez

Reviewer's Conclusions

Authors' conclusions 

Implications for practice 

In different countries, it has been documented that there has been a progressive increase in the rates of skin cancer (Lomas 2012; Sánchez 2011), driving the implementation of strategies that may help to control this growing phenomenon. The present systematic review explored the evidence related to the effect of sun protection measures against the occurrence of new cases of keratinocyte cancer, but was unable to find evidence for the effectiveness of sunscreen to prevent the development of basal cell carcinoma lesions (BCC) or cutaneous squamous cell carcinoma (cSCC) in the participants (Green 1999).

Implications for research 

Despite the fact that well‐planned studies need to be performed to address the main objective of this review, the widespread use of sunscreen may make it more difficult to run clinical trials where placebo creams are used as the control. However, other important questions remain, such as the optimal application frequency and minimum sun protection factor for the adequate prevention of cSCC and BCC, as well as the safety of the different sunscreen brands and their effects when applied to the skin. Future studies should also include histological confirmation of keratinocyte cancer (KC) cases, in order to obtain an accurate estimation of incident cases of cSCC or BCC, as well as the harms and possible adverse effects related to reduced sun exposure, such as vitamin D deficiency and depression.

Another difficulty is the proper monitoring of participants, with sufficient time to fully identify incident cases, which in the case of BCC could be longer than for cSCC. Population studies should be designed to assess follow‐up periods longer than 10 years to establish the effectiveness of sunscreen in preventing KC, because current studies have had short follow‐up periods. Although these short‐term outcome variables could be assumed as "proxy" in the incidence of KC, they do not allow for the generation of definitive conclusions given that they provide insufficient evidence. In addition, it would be worthwhile to evaluate the effect of multiple barrier measures combined with the use of sunscreen. It is important to remark that the design and conduct of these interventions need to be delivered within a suitable behavioural change framework. Such complex interventions require understanding the lessons learned from existing educational campaigns and behavioural motivation studies in these areas.

With regard to other protective measures (such as wearing sun‐protective clothing, glasses, or hats, or seeking the shade when outdoors), clinical studies need to be developed to evaluate their effectiveness and safety. These could be carried out in combination with the use of sunscreens and also in special groups, such as children or those with predominant skin phototypes I to III who have a higher risk of developing skin cancers.

The design of future studies in sun protection might be improved with the following suggestions.

• Evaluating different sun protection factors and different application regimens in order to establish what is the best sunscreen regimen to avoid onset of KC.
• Combining different sun protection strategies compared with sunscreen use in order to assess their effectiveness and safety.
• Comparing other sun protection strategies (such as wearing sun‐protective clothing, glasses, or hats, and seeking the shade when outdoors) versus sunscreen in order to assess whether there are differences between these interventions in terms of effectiveness and safety.
• Running campaigns to prevent skin cancer in different populations, especially those including the predominant skin phototypes I to III who have a higher risk of developing it.
• Adding adverse events as an important endpoint in the assessment of all of these preventive strategies.

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