Total exposure - not just sunburn - called key to cancer

WASHINGTON - Shade your kids. Strong new evidence suggests overall sun exposure in childhood, not just burns, is a key to who later develops deadly skin cancer.

The news comes as the government is finishing long-awaited new sunscreen rules.

The Food and Drug Administration wants sunscreens to be rated not just for how well they block the ultraviolet-B rays that cause sunburn - today's SPF rankings - but for how well they protect against deeper-penetrating ultraviolet-A rays that are linked to cancer and wrinkles.

The proposed rules are undergoing a final review and should be issued in weeks, FDA policy director Jeff Shuren said. The proposal will be followed by a public-comment period before taking effect.

New research into how the sun and genetics interact points to a possibly more important step consumers can take now to shield their children, and themselves: Check the local weather forecast for the day's "UV index" - or enter your ZIP code at http://go.philly.com/uv - to learn when to stay inside.

Why? Where you live - not the every-so-often beach vacation - determines most of your UV exposure. It comes on that lunchtime stroll, children's school recess or ball practice. UVA can even penetrate window glass.

UV levels vary from state to state and day to day, depending on altitude, cloud cover and ozone.

"Sunscreen is imperfect," warns Nancy Thomas, a dermatologist at the University of North Carolina who led the UV research. "Schedule activities when UV irradiation is not quite so high."

Melanoma is the most lethal skin cancer. It will strike almost 60,000 Americans this year, and kill 8,100. Cases have been rising for three decades, and while it usually strikes in the 40s or 50s, doctors are seeing ever-younger cases, occasionally even in children.

Scientists are studying the interaction of genes and UV exposure in melanoma patients, and initial results suggest staying in the shade in early life is even more important than previously realized.

Thomas analyzed tumor genes from 214 melanoma patients now living in North Carolina. Colleagues at the National Center for Atmospheric Research in Boulder, Colo., used satellite data to track average UV radiation - encompassing both UVA and UVB rays - in the towns and states where those patients had lived at birth, age 10, age 20 and so on.

The result: Patients with the most common known melanoma mutations, called BRAF mutations, also had the highest UV exposure by age 20. Interestingly, they also had the most moles, another big melanoma risk factor.

What does that mean? It's not clear yet, but young, rapidly growing skin may be particularly vulnerable to damaging UV rays, especially as moles are developing, Thomas says. Or maybe early childhood sun exposure spurs moles to start to develop.

While sun exposure for young adults played some role, too, the association with BRAF disappeared at age 30.

But that isn't a license for adults to sunbathe: Another melanoma subtype, characterized by mutations in a gene called NRAS, is strongly linked to UV exposure by age 50, the study found.

The problem: Until recently, sunscreens filtered out mostly UVB rays that cause sunburns - not UVA rays - meaning those who relied mainly on sunscreen to prevent cancer may have gotten a false sense of security.

Today, many sunscreens promise "broad-spectrum" protection against UVA rays, too. But the government does not yet have testing requirements in place to prove that UVA protection.