Regular use of sunscreen during a clinical trial of basal cell and squamous cell carcinomas was found to reduce the incidence of a different skin malignancy – new primary melanomas – up to 10 years later, according to a study published online Dec. 6 in the Journal of Clinical Oncology.
The number of invasive melanomas in particular decreased by 73%, but this was an exploratory finding "and should be interpreted cautiously," said Dr. Adéle C. Green and her associates at the Queensland Institute of Medical Research, Royal Brisbane (Australia) Hospital.
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The original clinical trial, conducted in 1992-1996 and involving 1,621 white Queensland residents aged 25-75 years at baseline, examined the effects of 5 years of sunscreen application and beta-carotene supplementation on the incidence of basal and squamous cell carcinoma.
Dr. Green and her colleagues new report focuses on the incidence of melanoma as a secondary end point in the same study population. "Despite the known etiologic role of sun exposure, the question regarding sunscreen use to prevent melanoma remains open and controversial," they noted.
During the trial, 812 patients were given a free, unlimited supply of SPF-16 sunscreen and instructed to use it daily on their head, neck, arms, and hands. A comparison group of 809 patients was randomly assigned to continue using sunscreen of any SPF at their own discretion, which included no use at all in 38% and infrequent use in another 35%.
The two groups were similar in established risk factors for skin cancer, degree of sun exposure, and use of sun protection measures other than sunscreen.
Between baseline in 1992 and the end of the extended follow-up in 2006, 36 study patients developed first primary melanomas. These were in-situ malignancies in 22 subjects and invasive in 14; none of the melanomas was metastatic. Three patients who had melanoma diagnosed in 1992 were excluded.
Only 11 subjects in the sunscreen group developed melanoma, compared with 22 in the comparison group. "Risk of melanoma overall was reduced in those randomly assigned to daily sunscreen compared with discretionary use, although the result was of borderline statistical significance," the investigators reported (J. Clin. Oncol. 2010 [doi:10.1200/JCO.2010.28.7078]).
The average melanoma thickness was 0.53 mm in the sunscreen group, compared with 1.2 mm in the comparison group. The incidence of invasive melanoma was decreased by 73% with sunscreen, while the incidence of in situ lesions was not significantly different between the two groups.
Melanoma incidence was decreased at all sites on the body, not just on the sites assigned to protection by sunscreen. This is probably because many study patients in the sunscreen group applied sunscreen to their trunks and lower limbs regularly, even though they had not been instructed to do so, Dr. Green and her associates noted.
"Our findings provide reassurance in view of the widespread uncertainty to date about sunscreen's ability to prevent melanoma," they reported.
"Although the results are directly relevant to people who live in sunny climates like Australia’s and who receive relatively high levels of ambient sun exposure as a matter of course, they also have implications for white people living in temperate climates in North America and Europe who are at increased risk of melanoma because of increased solar UV exposure caused by the predilection for holidays in sunny places," they concluded.