Don't chance it -- slather on the sunscreen

MEDICAL MATTERS

July 14, 2006|By JUDY FOREMAN

The American Academy of Dermatology, on its Web site, recently reaffirmed its message, saying that "scientific evidence supports the beneficial effects of proper sunscreen usage."

The American Cancer Society recommends using "a sunscreen with a sun protection factor (SPF) of 15 or higher." So does the government's Centers for Disease Control and Prevention.

But, in this era of evidence-based medicine, I have three nagging questions:

How much should I really worry about skin cancer?

How tightly linked are sun exposure and skin cancer?

How good is the evidence that sunscreens can protect me from skin cancer?

The answers, I have discovered, are complex, but are tipping me toward more diligent sunscreen use.

To be sure, skin cancer is not among the 10 leading causes of cancer deaths, according to 2006 projections by the American Cancer Society. But melanoma will be diagnosed in 62,190 people this year and kill 7,910. It would kill many more if it weren't caught and treated early. The incidence is rising, though more slowly than in the past.

This year there will be more than 1 million cases of basal and squamous cell cancers, which often occur in sun-exposed areas of skin, such as the face, neck and hands. Most of these are curable because they, too, are usually caught early. But removing cancers, especially from the face, can be disfiguring.

Question No. 2: the sun exposure link.

For squamous cell cancer, that's a no-brainer. "There is a very direct relationship between the amount of sun exposure over a lifetime and the development of squamous cell cancer," said Marianne Berwick, chief of the division of epidemiology and biostatistics at the University of New Mexico.

Dr. Martin A. Weinstock, a Brown University dermatologist and chairman of the skin cancer advisory group for the American Cancer Society, said squamous cell cancer can be triggered by two kinds of ultraviolet light: UVB and, to a lesser extent, UVA. Moreover, actinic keratoses - reddish patches on the skin linked to sun exposure - are now seen as precursors to squamous cell cancer.

The links between sun exposure and the other two skin cancers are trickier to sort out. "Nobody knows much about basal cell cancer," Berwick said.

But the real mystery is melanoma.

"There is definitely a debate about how much melanoma is linked to the sun. The majority of dermatologists feel it is partially linked to the sun," said Dr. Rebecca Kazin, an associate professor of dermatology at the Johns Hopkins University School of Medicine.

"It has a large genetic component as well," she said, with melanoma often running in families.

In a combined analysis of three large studies published in the Journal of Clinical Oncology last year, Harvard researchers listed the risks for melanoma in the following order: Older age, male, family history of melanoma, high number of moles, history of severe sunburn and light-colored hair. In other words, sun is one factor among many.

Patterns and risk

In addition to debating how big a role sun exposure plays in melanoma, researchers are not sure what pattern of exposure confers the most risk. Some say it's intermittent exposure - such as when pale workaholics spend a week in the Caribbean scorching their skin.

But age at which someone is exposed to the sun is important, too. When people migrate before age 15 from the rainy United Kingdom to sunnier Australia, they end up with a higher risk of melanoma, similar to native Australians, Weinstock said. If they migrate later, their risk is low, like the British, suggesting that childhood exposure is a major factor.

And then there's sunscreens. The evidence for sunscreen's protection depends on the type of skin cancer involved.

For squamous cell cancer, the evidence that sunscreen protects "is so strong that there is essentially no room for reasonable doubt," said Brown University's Weinstock. One persuasive study was a 1999 randomized, controlled trial of nearly 1,400 people in Australia, which found that sunscreens were protective against squamous cell cancers.

For basal cell protection, Weinstock called the evidence for sunscreens "substantial but indirect, and not sufficient to provide proof." For melanoma, he said, the case for sunscreen efficacy "is strong, but not definitive proof."

Over the years, European research has suggested that sunscreen use could actually increase the risk of developing skin cancer. The reason: by delaying sunburn, it might encourage people to spend more time in the sun.

But for melanoma, at least, a meta-analysis of data on 9,000 people published in 2002 in the American Journal of Public Health concluded that there was no increased risk linked to sunscreen use. A separate review of 18 studies in 2003 went further, finding no relationship - good or bad - between sunscreen use and melanoma.

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