Comment on sunscreen use and melanoma risk

Some studies demonstrate a positive association between sunscreen use and risk for cutaneous melanoma whereas others do not. Many confounding factors prevented any firm conclusions as to the possible protective or harmful effect on the use of sunscreens. The most likely reason for an apparently increased risk is that individuals who use sunscreen stay in the sun longer because they falsely believe that sunscreen protects them. This needs further research, particularly to clarify knowledge and attitudes to suntanning, sunscreen use and knowledge of skin cancer. It would seem that individuals intent on gaining a suntan use sunscreens to give themselves more time in the sun without sunburn. Reducing their risk of cancer is a secondary motive. Risk is also related to phenotype and history of sun exposure and sunburn. There is equivocal evidence about the use of sunscreen and the use of other photo-protective measures. Further research is needed to assess these factors in long-term randomised studies with specific target groups. Such research needs to include a formative stage that seeks to explore knowledge and attitude to sunscreen use and other photo-protective measures. This information will enable specific outcome objectives to be developed for each aspect of the study, thus reducing confounding factors. There is a need for an agreed definition of "sunscreen use" and specific definition and description of such use: how, when and what SPF is used in specific situations.

The Nambour Skin Cancer Prevention Trial (a randomised study exploring risk of both SCC and BCC) demonstrated that sunscreen use could be significant in reducing the risk of SCC.44 This was a complex trial including 1850 residents aged 20-69. They were invited to use a daily application of SPF 16 sunscreen and use 30 mg of beta-carotene supplement in the prevention of skin cancer; 1647 attended baseline assessment that included a cancer risk factor assessment and a full skin examination by a dermatologist. Any detected skin cancers were removed at the start of the study. Out of these 1647 residents, 1621 agreed to take part in the study. They were randomised to one of four study groups, sunscreen and beta-carotene; sunscreen and placebo; no sunscreen and beta-carotene; and no sunscreen and placebo. The participants attended a clinic every 3 months to receive new sunscreen and beta-carotene. The weight of the sunscreen returned to these clinics every three months was recorded. A random subgroup of sunscreen users kept a 7-day diary on three occasions to record their frequency of sunscreen application and sun exposure. Dermatologist examinations were given at these visits and any cancers removed and recorded. No protective effect for prevention of SCC was found in the beta-carotene group. Sunscreen use was analysed for all groups, regardless of beta-carotene use as no interaction was seen between the two interventions (sunscreen and beta-carotene). A total of 28 new SCCs were detected in the group given sunscreen and 46 in those not given sunscreen (RR, 0-61; 95% CI 0-50-1-6) a statistically significant difference. The authors concluded that sunscreen use could be of significant benefit in protecting against SCC. No placebo sunscreen was used and the results need to be interpreted with caution because the comparison group was not ideal, reducing the power of the study to detect an effect of daily sunscreen use. Green et al. (1999)45 subsequently reported that solar exposure of those given sunscreen did not differ from those not given sunscreen. The prevalence of sunburn was lower for those receiving sunscreen to those not receiving it (tested on a random sample of participants wearing photosensitive badges). The findings suggest that the reduction of incidence of SCC seen in the group using sunscreens was probably due to the attenuation [sic thinning] of the UVR by the sunscreen rather than in behaviour change (reducing time in the sun). Higher factor sunscreen use, especially for older people, may not result in them spending longer time in the sun.

A cohort study by Grodestein et al. (1995)46 reported that sunscreens used over a 2-year period by women who spent 8 or more hours per week in the sun was not protective by comparison with no use of such agents (RR 1-1; 95% CI 0-83-1-7).

Timing of exposure to UVR was a significant risk factor for SCC in a case-control study by Pogoda

Can the use of sunscreen reduce the risk of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC)?

and Preston-Martin (19 96).47 There is little evidence that sunscreen use protects against BCC. Some patients may have been advised to use sunscreens following diagnosis, which may have confounded results. Following diagnosis of SCC, use of sunscreen was examined retrospectively in three age groups: 8-14, 15-19 and 20-24 years. Those in the 8-14 group who had used sunscreens seemed to have a slightly reduced risk of SCC (RR 0-61; 95% CI 0-82-4-4) not statistically significant. Those using sunscreen in the 15-19 age group had a relative risk of 1-9 (95% CI 0-82-4-4) and those in the 20-24 group had a risk of 0-99 (95% CI 0-44-2-2). No strong protective effect of sunscreens was found.

One cohort, Hunter et al. (1990)48 and one case-control study by Kricker et al. (1995)49 reported increased risks for BCC in sunscreen users. No significant association between sunscreen use and cancer risk was observed in one cohort and one case-control study of SCC50, one of SCC and BCC of the skin or one case-control study of SCC of the vermilion border of the lip.47 Confounding of sun sensitivity and exposure were present in these studies, as in previously described studies.

Kricker et al.49 found that subjects who had used sunscreens for at least half the time spent in the sun 1-9 years prior to diagnosis had a higher relative risk for BCC than those who had never used sunscreens or had used them less than half the time (RR 1-8; 95% CI 1-1-2-9). This risk persisted after adjustment for age, sex, ability to tan and site of lesion. No change in RR was found for those who had used sunscreens more than half the time in the 1-9 years, prior to diagnosis (RR 1-1; 95% CI 0-69-1-7) in comparison to those who had not used sunscreens or who had used them for half the time. Few subjects had access to sunscreens 11-30 years before diagnosis.

Studies that have used intermediate end points such as incidence of solar keratoses as markers for basal and SCCs risk

Actinic (solar) keratoses are a risk factor for BCC and a precursor lesion for SCC. They are related to solar exposure and phenotype. The rate of development for SCC is low and many regress spontaneously, especially when exposure to UVR is reduced. These lesions have therefore been used as an intermediate endpoint in studies on the use of sunscreens in the prevention of SCC.47,51 The Maryborough Trial in Australia51 assessed whether the daily use of sunscreen had any effect in reducing the development of actinic keratoses in those already having these. This was a short-term study using a placebo and included body site examination and diaries to record the time of day patients applied sunscreen. Those using placebo had greater mean increase in the number of keratoses during the study (1-0 ± 0-3 SE) than those given sunscreen (0-6 ± 0-3; RR 1-5; 95% CI 0-81-2-2). Fewer new keratoses were found in the sunscreen group (1-6 versus 2-3 lesions per subject; RR 0-62; 95% CI 0-54-0-71). After controlling for sex and sun sensitivity, the likely remission of keratoses (those with keratoses at the start of study) was greater for the sunscreen group (25% versus 18% initial lesions regressing: RR 1-5, 95% CI 1-3-1-8.51

Comment on sunscreen use and BCC and SCC

There is no conclusive evidence that sunscreen protects against either SCC or BCC and there is some limited evidence to suggest that risk may increase with sunscreen use. However, these non-randomised studies had confounding variables that make it difficult to be conclusive about such evidence.

Although the Maryborough acitinic keratoses trial51 was a short-term trial, the confounding factors were well accounted for. The study suggests that sunscreen can prevent the development of new actinic keratoses. Further research is required to provide conclusive evidence of these results.

A number of studies have assessed the effectiveness of targeted sun protection interventions combined with sunscreen use.52-79 Sunscreen use is only one of many outcome measures in these multistrategic interventions targeted at specific groups or to communities in general but was reported separately. Seven studies54'55,60,61'68'71'72 were conducted in schools; four at beaches52,57,63,69; two at pools52'75 and three in other recreational settings.62,65,67; There were two studies in the workplace69,72; and two in clinical/medical settings.58,61 There was one study in the tourist industry53 and four multicomponent community studies.56,66,70,73 Most studies were short term and aimed at improving sun-protection behaviour among specific high-risk groups, including children, young people, beachgoers, outdoor workers and patients with non-melanoma skin cancers.

In the main the studies used interactive educational presentations and communication strategies including peer-led programmes, role modelling, parental activities and materials aimed at increasing knowledge, including specific recommendations for sunscreen use. Interventions to enable policy change such as developing social and physical environments (shaded areas) for sun protection were the focus of three interventions.52,60,73 Parental activities62 and home activities61 were the focus of two interventions. Medical interventions mainly used information giving to raise awareness of primary and secondary prevention of skin cancer.56,58,60

More complex community interventions used incentives for beach guards, booklets52,56,61, primary and secondary prevention information and education,66,73-76,79 and in schools.54,55,6771,73

Twenty-two studies, quasirandomised and longitudinal studies reported on at least one outcome measure with regard to sunscreen use; proxy measures for behaviour were used in some studies (for example, the intention to use sunscreen). Eleven out of sixteen targeted interventions were successful in increasing knowledge and behaviour52,54,56,59,61-64 and six were successful in increasing solar potection, either the use of shade, staying out of the sun or the use of clothing52-59,62,64,68,73 and increased sunscreen use.52'54'56-58'62'64'65'66-69 The duration and intensity of the intervention affected the success of the intervention. Successful interventions were longer, had multiple components or were supported by broader community initiatives.

Other reported successful educational intervention strategies were those intended to increase the perception of risk for developing skin cancer. Strategies that involved showing young people computer photoimages of their own faces with superimposed ageing and images of skin lesion were successful in improving both the frequency of sunscreen use and the application of sunscreen.65

An intervention for outdoor workers increased the use of sun protection but the use of sunscreen was not reported separately.69 The impact of an intervention at swimming pools in which clients were given incentives and exposed to role modelling of lifeguards is unclear, although the authors reported that the sun-protection score was improved when two or more sun-protection measures were taken together, with no change in the mean quantity of free sunscreen used at pools.52

Do multistrategy interventions increase intention to use sunscreens as a protective measure for reducing the risk of melanoma and non-melanocytic skin cancers?

There have been six reported community interventions aimed at improving knowledge of skin cancer, encouraging the use of protective clothing and sunscreen use74-79 Experience suggests that they require long-term funding, commitment and evaluation. Cross-sectional population surveys included the "Slip, Slap, Slop" and "SunSmart" campaigns in Australia74,75; "Sun Awareness" in Canada76; UVR index forecasting in the US71; the Melanoma and Skin Cancer Detection and Prevention programme in the US72; and the Falmouth Safe Skin Programme in the US.77 These were aimed at improving community knowledge about skin cancer and sun protection, and included mass media components, distribution of educational leaflets, the development of school curriculum for sun protection and sometimes partnership working in locality settings. Five of these large-scale community interventions had a positive impact on sunscreen use at population level.74-79 The UVR index study reported no effect on sunscreen use but sunscreen use was associated with increased awareness of weather forecasts.71,72

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