A topic in Clinical Evidence 3 summarizes the results of one RCT (1621 adults in a subtropical community in Australia). It found that daily use of sunscreen compared to usual discretionary use reduced the incidence of squamous cell carcinoma after 4.5 years (22 people with 28 new squamous cell carcinomas with daily sunscreen vs 25 people with 46 new squamous cell carcinomas with discretionary sunscreen use, RR 0.61, 95% CI 0.46 to 0.81). The incidence of solar keratoses was reduced (increase in solar keratoses 20% with daily sunscreen vs 57% with discretionary use, p<0.05).
In a randomized, controlled trial of the effect on solar keratoses of daily use of a broad-spectrum sunscreen cream with a sun-protection factor of 17 in 588 people 40 years of age or older in Australia during one summer, the subjects applied either a sunscreen cream or the base cream minus the active ingredients of the sunscreen to the head, neck, forearms and hands 1. The mean number of solar keratoses increased by 1.0 per subject in the base-cream group and decreased by 0.6 in the sunscreen group (difference, 1.53; 95% confidence interval, 0.81 to 2.25). The sunscreen group had fewer new lesions (rate ratio, 0.62; 95% confidence interval, 0.54 to 0.71) and more remissions (odds ratio, 1.53; 95% confidence interval, 1.29 to 1.80) than the base-cream group. There was a dose-response relationship.
A controlled trial was undertaken from December 1987 to December 1990 to test the hypothesis that a strong sunscreen can reduce the number of cancerous and precancerous skin lesions. Candidates were selected from a high-risk population attending either a university- or Veterans Affairs -based dermatology practice in Lubbock, Texas 2. In a prospective, double-blind, controlled trial of daily application of sunscreen vs. placebo over a 2-year period in patients who had demonstrated pre-malignant changes (actinic keratoses) or non-melanoma skin cancer (basal cell carcinoma or squamous cell carcinoma), had continuing sun exposure, and were not using sunscreen on a regular basis, 53 volunteers were initially enrolled in the study, and 37 came for the final 24-month visit 1. The rate of appearance of new precancerous skin lesions was lower among the treatment group than among the control subjects. The numbers of new non-melanoma skin cancers appearing during the study period were too small for statistical analysis.
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