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Skin Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Description of the Evidence

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One very small randomized placebo-controlled study of a sunscreen (sun protection factor [SPF] 29) was conducted in 53 volunteers who had either clinical evidence of solar keratoses or NMSC.[14] Only 37 of the participants returned for the planned 2-year follow-up (attrition rate of 30%). The rate of new solar keratoses was lower after 2 years in the sunscreen group than in the placebo (base-cream) group (estimated 36% reduction in annual rate, P = .001). Another study showed that regular sunscreen use helps reduce the incidence of solar keratoses and increase remission of existing lesions.[15] In Australia, 588 persons aged 40 years and older who attended a free skin-cancer screening clinic and had 1 to 30 solar keratoses were enrolled in a randomized controlled trial (RCT) assessing the effect of regular sunscreen (SPF 17) use on solar keratoses; 431 persons completed the study. Individuals in the sunscreen group developed fewer new lesions and had more remissions of existing lesions than those in the base-cream placebo group. There was an increase of 1.0 in the mean number of solar keratoses in the base-cream group versus a decrease of 0.6 in the sunscreen group (difference = 1.53; 95% confidence interval [CI], 0.81–2.25). The rate ratio of new lesions was 0.62 (95% CI, 0.54–0.71). Furthermore, in the sunscreen group, the development of new lesions and the remission of existing lesions were related to the amount of sunscreen used. Such a relationship was not observed in the base-cream group.

However, a different Australian randomized study (the Nambour Skin Cancer Prevention Trial) showed that, after 4.5 years of follow-up, there was no statistically significant difference in the incidence of BCCs or SCCs with regular SPF 16 sunscreen use. This study did not include a sunscreen placebo. Although a secondary subset analysis of the overall number of tumors showed a reduction in the frequency of SCCs on the sites of daily sunscreen application, the validity of the finding is questionable because of the possible effects of extensive multiple statistical testing.[16] An 8-year post-trial observational follow-up demonstrated statistically significant reductions in both the frequency and the overall incidence of SCCs in the regular sunscreen-use arm, but the reliability of these findings is uncertain given their occurrence outside of the controlled-trial environment.[17]

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