AMSTERDAM — A landmark Australian study has provided the first glimmer of evidence that daily sunscreen use might reduce the incidence of both basal cell carcinoma and melanoma years later, Dr. Adele Green reported at the 11th World Congress on Cancers of the Skin.

This same community-based clinical trial, the Nambour Skin Cancer Study, also showed far more convincingly that 4.5 years of daily sunscreen application resulted in a highly significant 38% reduction in the incidence of squamous cell carcinoma (SCC), compared with discretionary use of sunscreen. This benefit persisted—and actually even increased in magnitude—for 8 years after the end of the intervention, said Dr. Green, head of the cancer and population studies group at the Queensland Institute of Medical Research, Brisbane.

Nambour is a subtropical Australian community with skin cancer rates that are among the world's highest. The Nambour study involved 1,621 adults who in 1992 were randomized to 4.5 years of daily application of a broad-spectrum SPF 17 sunscreen to the head, neck, forearms, and hands, or to a control group in which sunscreen use was discretionary and less frequent.

During 1993–2005, 21 melanomas—8 in the intervention group and 13 in controls—were diagnosed on target skin areas during blinded skin exams. That translated into incidence rates of 70 and 113 cases per 100,000 person-years, respectively, for an intriguing, albeit statistically nonsignificant, 39% relative risk reduction for melanoma in the daily sunscreen group, she noted.

“The likelihood that we'd see enough melanomas in a community study to reach firm conclusions was always slim. If we had a trial about 100 times this size, we might have been able to bring the confidence limits down to reach significance. But this is the first suggestive evidence we've ever had from an intervention trial showing a protective effect of sunscreen on melanoma,” Dr. Green said at the meeting, which was sponsored by the Skin Cancer Foundation.

And, for reasons both ethical and practical, it is probably the only large sunscreen intervention trial in melanoma that will ever be done, given that the study convincingly showed that daily application prevents SCCs, she noted.

There was a nonsignificant 13% relative risk reduction in histologically confirmed basal cell carcinomas (BCCs) during 1993–2004 in the intervention group.

During late follow-up in 2001–2004, fully 5–8 years after the intervention ended, the BCC rate was 2,548 per 100,000 person-years in the intervention group and 3,408 per 100,000 person-years in controls. That's an adjusted 25% relative risk reduction—again, not statistically significant, but getting closer, as would be anticipated if BCCs have a more prolonged pathogenesis than do SCCs.

“I suspect if the intervention started earlier in life and continued for longer we'd see more definitive results,” Dr. Green continued.

An increased late benefit for daily sunscreen use was well documented with regard to SCC prevention.

During late follow-up in 2001–2004, there were 29 histologically confirmed SCCs in the intervention group and 59 confirmed in controls, for a highly significant 51% reduction in relative risk, compared with the 38% reduction for 1993–2004.

A second line of evidence suggesting that sunscreen protects against BCC comes from an analysis of study participants who had more than one BCC during the intervention phase.

Second BCCs occurred at a mean of 30.8 months after the first in the daily sunscreen group, compared with a 25.7-month delay in controls. Third BCCs occurred a mean of 24 months after the second in the intervention arm and a mean of 19.3 months in controls. This worked out to an adjusted 30% retardation in the occurrence of a second BCC, and a 41% delay for the third in the intervention arm.

Sun exposure during and after the intervention period was similar in both study arms. Of participants in the intervention arm, 25% used sunscreen regularly after the intervention period, as did 18% of controls, a modest difference that was adjusted for statistically.

Dr. Jean-Jacques Grob, professor of dermatology at the Université de la Méditerranée, Marseille, France, said that he believed that the Nambour trial was “the most important study ever done regarding sunscreens.”

Dr. Allan C. Halpern said that the long-term Nambour BCC and melanoma findings were the most important take-home findings.

“Many of us have thought all along that if one started sun protection early enough, it should have a delayed effect on BCC and melanoma, and Dr. Green's point estimates suggest that.

“There's no statistical significance, but I still think it's very interesting data. The confidence intervals are narrowing,” noted Dr. Halpern, who is the chief of the dermatology service at Memorial Sloan-Kettering Cancer Center, New York, and the cochairman of the National Council on Skin Cancer Prevention.

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'If the intervention started earlier in life and continued for longer we [might have seen] more definitive results.' DR. GREEN

Daily Sunscreen May Block Later BCC, Melanoma : Data from an Australian clinical trial offer the first evidence of a protective effect against skin cancer.