Year-Round Sunscreen and the Prevention of Skin Cancer
October 30, 1999
Year-Round Sunscreen and the Prevention of Skin Cancer
Abstract & commentary
Synopsis: In this report, community volunteers in Australia were randomly assigned to one of four groups and received either sunscreen daily or no sunscreen daily, with or without the orally administered anti-oxidant, beta-carotene.
Source: Green A, et al. Lancet 1999;354:723-729.
The application of sunscreen can prevent sunburn, but the question of whether long-term use can prevent skin cancer has not been resolved. The purpose of the current study was to assess whether sunscreen use prevents skin cancer. Additionally, intake of the dietary anti-oxidant beta-carotene was also tested to determine if it too could prevent skin cancers. Individuals (n = 1621) from a single community in Nambour, Australia, were randomly assigned into one of four groups:
• sunscreen to sun-exposed areas plus oral beta-carotene;
• no sunscreen plus oral beta-carotene;
• sunscreen plus oral placebo; or
• no sunscreen plus oral placebo.
The sunscreen strength was SPF-15 and was applied daily to the head, neck, arms, and hands. The beta-carotene was formulated to a single daily, oral dose of 30 mg. The median age of participants was 49 years and there were no clinical differences among the groups before the initiation of treatment. The treatment continued for 4.5 years and participants were examined every three months for skin evaluation and distribution of study materials. Compliance was measured and found to be good. Over the length of the study, the attrition rate was approximately 15% and this affected all four study groups equally.
Over the study period, 250 individuals developed 758 new skin cancers. There were no significant differences in the incidence of first new skin cancers in the four groups. However, in terms of number of tumors, the incidence of squamous-cell carcinoma was significantly lower in the sunscreen group than in the no-sunscreen group (1115 vs 1832 per 100,000; rate ratio 0.61 [95% CI 0.46-0.81]). This protection by sunscreen was not apparent for the development of basal-cell carcinoma and there was no protection against either squamous-cell or basal-cell carcinoma provided by oral beta-carotene.
Comment by Dan Longo, MD
Every once in a while, well-constructed clinical trials produce results that conform with conventional wisdom. After all, sunscreens are known to block ultraviolet (UV) rays and these are known to be carcinogenic.1,2 Furthermore, sunscreens are safe and well tolerated and clearly prevent sunburn. Epidemiological studies have shown an association between sunburn and skin cancer.3 Thus, it stands to reason that sunscreen applied chronically would prevent skin cancer and, indeed, that was observed.
The observation that basal-cell carcinomas were not reduced in this group may impart some insight into the biology of this indolent type of tumor. Perhaps these too would have been prevented in a study of more than 4.5 years duration. Similarly, beta-carotene, which has diminished the incidence of UV-light-induced tumors in mice, was shown not to influence the incidence of basal- cell or squamous-cell carcinomas in this study.4
Sunscreen is an inexpensive form of cancer prevention, especially when compared to other interventions. In Australia, where skin cancer rates historically have been high, a well-coordinated national effort has already been associated with a decline in new cases. But the effort includes more than just sunscreen. Aggressive public education campaigns, avoidance of sun exposure in peak hours, appropriate clothing (including hats), and government-sponsored dispensing of sunscreen at public beaches and parks are all components in this effort.
The question of which level sunblock is recommended is also addressed by the Australians. SPF-15 blocks approximately 94% of solar UV rays and increments above that are associated with both increased expense and cutaneous allergic response.5 Furthermore, in a recent report in the Journal of the National Cancer Institute, investigators found that volunteers randomly assigned to receive SPF-30 sunscreen spent more recreational time in the sun when compared to those who received SPF-15. This was a blinded trial and participants did not know which of the sunblocks they received. Presumably, recreational sun exposure was increased due to less acute skin injury (sunburn). This could explain the puzzling, previously reported observation that sunscreen users seem to have higher rates of at least some skin cancers, such as melanoma.6 Surveys have also reported (as did the JNCI paper) that individuals rarely apply the recommended amount of sunscreen.7
Thus, this report finally provides evidence that application of sunscreen prevents skin cancers. The incidence of squamous-cell carcinomas was less in those randomly assigned to apply SPF-15 daily for 4.5 years. Perhaps future studies of longer duration will show that basal-cell cancers and melanomas will be similarly prevented. However, it is also possible that the commercial sunblocks are not effective at blocking out the component of sun exposure that is etiologic in basal-cell carcinoma and melanoma. The best preventive measure for skin cancer at present is not just to block the sun with sunscreen, but to stay out of the sun, if at all possible. It is hoped that further study will identify the culprit responsible for the increased incidence of melanoma. (Dr. Longo is Scientific Director, National Institute on Aging Baltimore, MD.)
References
1. Kligman LH, et al. J Am Acad Dermatol 1980;3:30-35.
2. Blum FH, et al. JNCI 1941;3:259-268.
3. Kricker A, et al. Cancer Causes Control 1994:5: 367-392.
4. Lambert LA, et al. Nutr Cancer 1994;21:1-12.
5. Emmons KM, Colditz GA. J Natl Cancer Inst 1999; 91:1269-1270.
6. English D, et al. Cancer Causes Control 1997;8: 271-283.
7. Autier P, et al. J Natl Cancer Inst 1999;91:1304-1309.
Which one of the following statements about prevention of skin cancer is true?
a. Regular daily use of SPF-15 sunblock for 4.5 years has been shown to reduce the incidence of all forms of skin cancer.
b. Regular daily use of SPF-15 sunblock for 4.5 years has been shown to reduce the incidence of melanoma but not basal-cell or small-cell carcinoma.
c. Regular daily use of SPF-15 sunblock for 4.5 years has been shown to reduce the incidence of squamous-cell carcinoma but not melanoma or basal-cell carcinoma.
d. Regular daily use of SPF-15 sunblock for 4.5 years has not been shown to reduce the incidence of skin cancers.
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