40 SUN CARE
Preventing skin cancer: new technologies needed?
Norman E Miller, Irina P Miller - Kutanios
For many years, all common skin cancers - melanoma, squamous cell carcinoma (SCC), and basal cell carcinoma (BCC) - have been increasing worldwide in people with fair skin. Data from the UK and Poland are shown in Figure 1.1,2 In the USA, the incidence of SCC increased
2.45-fold during 1980-2005, and that of BCC 3.65-fold; during 1982-2011 melanomas rose twofold.3
More people now develop skin cancer
in USA than all other cancers combined, and one in five Americans will develop it by age 70 years.4-6
This has happened despite increasing sales
of sunscreens, and several improvements in formulation: increases in the SPF numbers of UVB filters, and the addition of UVA filters, antioxidants, stabilizers, and inorganic filters.7 Very little of the rise can be explained by the increase in UV penetration due to stratospheric ozone depletion.8,9 A failure by consumers to use sunscreens
regularly and to follow guidelines are part of the problem.10,11
Autier et al concluded that
using a sunscreen leads to increased intentional exposure to sunlight, increasing the dose of radiation received.12,13
and the first UV But is this the whole story? The only certain way to assess the efficacy of
a preventive agent is by clinical trials. Given that a causal effect of UV radiation on skin cancer was demonstrated in 1928,14
screen entered the market seven years later,15 it
is surprising that there has been only one long- term trial, the Nambour Study in Australia. This trial followed 1,621 adults for 4.5
years, during which half applied a sunscreen of SPF16 (containing UVB and UVA filters) to the head, face, arms and hands daily, and the rest continued with “discretionary use” of sunscreens.16 No reduction of BCC or SCC was observed; melanomas were too few for analysis. A subgroup who had additionally been given oral beta-carotene also showed no benefit. Participants were then monitored for another eight years, during which they followed their personal preferences for sunscreen use. After this time, the original treated group had
a 35% lower incidence of SCC, but there was still no reduction of BCC. As BCC accounted for 70% lesions, total non-melanoma incidence was reduced by 23%.17 Although another paper ten years after
completion of the trial reported fewer melanomas in the treated group (11 vs 22,
PERSONAL CARE April 2024
P = 0.051), when the analysis was confined to lesions in the prescribed regions, i.e. excluding legs and back, the difference was not significant.18 The results can be used to estimate the
potential impact of regular use of a similar UV screen in the USA, where there are respectively 3.6, 1.8, and 0.19 million cases of BCC, SCC, and melanoma annually.3,4 They suggest that about 15% of all skin cancers
would be prevented. Although most current UV screens have SPF numbers exceeding 16, the improvement in filtration with increasing SPF is small, values of 15, 30, and 50 corresponding to 93, 97, and 98% attenuation of UVB.
Efficacy of UV screens Several observational studies have also
addressed the question of the efficacy of UV screens. A meta-analysis of 9,067 subjects in 11 case-control studies failed to demonstrate a protective effect against melanomas.19 A prospective population-based study of
143,844 Norwegian women found that those using an SPF≥15 UV screen had a 18% lower incidence of melanoma than those using SPF<15.20
Watts et al studied melanomas in
Australian adults before age 40 years.21 After adjusting for age, gender, history of sunburn, and other variables, regular sunscreen use since childhood was associated with a 40% lower risk. Gorham et al pooled data from 17 observational studies, and found no association of melanoma with sunscreen use.22 When the studies were separated according to latitude (greater or less than 40°), sunscreen
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