Daily sunscreen application and betacarotene supplementation in preventionof basal-cell and squamous-cell carcinomas of the skin: a randomised controlled trial

Background The use of sunscreens on the skin can prevent sunburn but whethe r long-term use can prevent skin cancer is not known. Also, there is eviden ce that oral betacarotene supplementation lowers skin-cancer rates in anima ls, but there is limited evidence of its effect in human beings. Methods In a community-based randomised trial with a 2 by 2 factorial desig n, individuals were assigned to four treatment groups: daily application of a sun protection factor 15-plus sunscreen to the head, neck, arms, and han ds, and betacarotene supplementation (30 mg per day); sunscreen plus placeb o tablets; betacarotene only; or placebo only. Participants were 1621 resid ents of Nambour in southeast Queensland, Australia. The endpoints after 4.5 years of follow-up were the incidence of basal-cell and squamous-cell carc inomas both in terms of people treated for newly diagnosed disease and in t erms of the numbers of tumours that occurred. Analysis of the effect of sun screen was based only on skin cancers that developed on sites of daily appl ication. All analyses were by intention to treat. Findings 1383 participants underwent full shin examination by a dermatologi st in the follow-up period. 250 of them developed 758 new skin cancers duri ng the follow-up period. There were no significant differences in the incid ence of first new shin cancers between groups randomly assigned daily sunsc reen and no daily sunscreen (basal-cell carcinoma 2588 vs 2509 per 100 000; rate ratio 1.03 [95% CI 0.73-1.46]; squamous-cell carcinoma 876 vs 996 per 100 000; rate ratio 0.88 [0.50-1.56]). Similarly, there was no significant difference between the betacarotene and placebo groups in incidence of eit her cancer (basal-cell carcinoma 3954 vs 3806 per 100 000; 1.04 [0.73-1.27] ; squamous-cell carcinoma 1508 vs 1146 per 100 000; 1.35 [0.84-2.19]). In t erms of the number of tumours, there was no effect on incidence of basal-ce ll carcinoma by sunscreen use or by betacarotene but the incidence of squam ous-cell carcinoma was significantly lower in the sunscreen group than in t he no daily sunscreen group (1115 vs 1832 per 100 000; 0.61 [0.46-0.81]). Interpretation There was no harmful effect of daily use of sunscreen in thi s medium-term study. Cutaneous squamous-cell carcinoma, but not basal-cell carcinoma seems to be amenable to prevention through the routine use of sun screen by adults for 4.5 years. There was no beneficial or harmful effect o n the rates of either type of skin cancer, as a result of betacarotene supp lementation.