SUNSCREEN USE SHOWN TO REDUCE INCIDENCE OF SOLAR KERATOSES

SUNSCREEN USE SHOWN TO REDUCE INCIDENCE OF SOLAR KERATOSES, a precursor of squamous-cell carcinoma of the skin, in a seven- month, controlled study conducted by Sandra Thompson, PhD, et al., which appears in the Oct. 14 edition of The New England Journal of Medicine. The researchers found a 38% reduction in the incidence of new keratotic lesions and an increased rate of remission of older lesions in the group using a sunscreen with an SPF 17 value. The researchers are affiliated with the University of Melbourne in Victoria, Australia. Thompson et al. concluded that "regular use of sunscreens prevents the development of solar keratoses and, by implication, possibly reduces the risk of skin cancer in the long term." The study enrolled 588 people aged 40 and over with prior solar keratoses living in the southeastern part of Australia in the state of Victoria. The participants were randomized to receive either a base-cream or a broad spectrum sunscreen containing 8% 2- ethyl-hexyl p-methoxycinnamate and 2% 4-tert-butyl-4-methoxy-4- dibenzoylmethane, which controls exposure to both ultraviolet A and B rays. The study participants were instructed to apply the cream every morning and during the day, as needed, during the Australian summer months from September 1991 to March 1992. A total of 431 subjects finished the study with 210 in the sunscreen group and 221 in the base-cream group. Dropouts split fairly evenly between study and control groups -- 103 versus 108 dropouts, respectively. "At the end of the study," the researchers noted, "there was a mean increase of 1.0 in the total number of solar keratoses per subject in the base-cream group as compared with a mean decrease of .6 lesions per subject in the sunscreen group." The study authors reported that a total of 333 new lesions occurred in the sunscreen group while a total of 508 new lesions were found in the base-cream group, which averaged out to 1.6 new lesions per subject in the sunscreen group versus 2.3 new lesions per subject in the control group. In addition, the study found that 25% of lesions present at the start of the study had remitted in the sunscreen group compared to 18% in the base-cream group. The study also shows evidence of a dose-response curve. The authors found that "both the number of new lesions and the probability of remission were affected by the amount of cream used." According to Thompson et al., "the number of new lesions was 23% of the number present at base line in the subjects who used less than 500 g of sunscreen [over the seven-month period], and it was 12% of base line among those who used more than 1,000 g." In addition, "there was no difference in the probability of remission between treatment groups if the subjects used less than 500 g," the researchers found, "but there was a clear difference when use exceeded 500 g." Noting that solar keratoses and nonmelanoma skin cancers are the most common dysplasias and cancers in the white population in many countries, the researchers suggested that the results of their study "confirm the appropriateness of the approach to this problem being taken by an increasing number of public health organizations in many countries; that is, they should continue to recommend the use of sunscreens in addition to other methods of protection from sunlight . . . to reduce the risk of skin exposure." In an editorial appearing in the same issue of NEJM, Barbara Gilchrest, MD, Boston University School of Medicine, suggested that the Australian study sends a positive message to those concerned about the epidemic of skin cancer among white people throughout the world, as well as to those interested in cancer prevention more generally." Gilchrest pointed out that "a simple intervention, used for a relatively brief period, appeared to decrease the risk of cancer, at least as measured by the diminution or disappearance of an intermediate marker." Weighing the potential hazards of using sunscreens with a high SPF, Gilchrest addressed concerns that such use could lead to vitamin D deficiency and cancer. She noted that "current opinion strongly supports the position . . . that whatever the potential protective effect of ultraviolet-induced syntheses of vitamin D on the progression of melanoma and other cancers, it is far outweighed by the well-established causative role of ultraviolet irradiation in skin cancer, including melanoma." "On balance," Gilchrest declared, "the possible adverse consequences of sunscreen use are dwarfed by their established benefits." Regarding cost, she pointed out that the amount of sunscreen recommended in the Australian study "requires an investment of approximately 25" per day for the prevention of skin cancer, painful sunburn, and cosmetically displeasing photodamage."