Thwarting skin cancer with sun sense
Skin cancer is the most prevalent of all cancer, and it's increasingly common.
"This looks like skin cancer," the dermatologist told the woman as he examined the spot on her leg. Later, after removing the tumor and several other precancerous growths from her face and hands, he looked her in the eyes and said, "You've had enough sun."
More and more people are hearing similar messages from their doctors. Viewed as an undeclared epidemic by dermatologists, skin cancer is the most prevalent of all cancers, and it's increasingly common. About a million Americans will develop skin cancer this year.
"Skin cancer is now about as common as all other cancers combined," says Martin A. Weinstock, M.D., Ph.D., director of Brown University's Dermatoepidemiology Unit and Chief of Dermatology at the Providence (R.I.) Veterans Affairs Medical Center. And there's no evidence that the epidemic has peaked.
But there is a bright side. Skin cancer is quite curable when treated early. More than 90 percent of skin cancers are completely cured. Even better, it's largely preventable, simply by avoiding sun and sunlamp exposure.
As more consumers become sun smart, they're finding new ways to protect themselves. For example, FDA has cleared for marketing one manufacturer's clothing for sun protection. Eating a healthier diet can't hurt--less fat, more fruits, vegetables and grains--and preliminary studies indicate it may help. And the National Weather Service provides a measure of ultraviolet (UV) exposure with its UV Index, which is part of the daily weather forecast for many cities.
Experts agree that sunlight, particularly the UV wavelengths, damages the skin. UV radiation causes the obvious short-term damage seen in a sunburn or a tan, as well as the long-term damage. Not only is there no such thing as a safe tan, "There's no known safe amount of sun," Weinstock says.
Americans are getting the message. Increasingly, we're protecting ourselves from the sun, according to a 1994 survey commissioned by the American Academy of Dermatology. But we're not all sun savvy yet. Only 2 in 5 people consistently use sunscreen whenever they're in the sun. Fewer people say they sun-bathe, but about 1 in 5 adults still does. And some people have the mistaken impression that sunlamps or tanning salons are somehow better or safer than natural sunlight. They aren't. No matter what the source, UV exposure increases your risk of skin cancer. (See "Sunlamps--Not a Bright Idea.")
There are three main types of skin cancer. Melanoma is the least common but most serious because this killer is responsible for three-quarters of the nearly 10,000 skin cancer deaths per year. The other two types--basal cell and squamous cell carcinomas--are often referred to together as non-melanoma skin cancer. Basal cell cancer is by far the most common skin cancer, followed by squamous cell carcinoma, which can also become a killer. Between 1980 and 1989, the incidence of non-melanoma skin cancers increased 65 percent, and melanoma 21 percent. And skin cancer is striking at ever younger ages. One-quarter of the more than 30,000 people expected to develop melanoma this year will be 39 or younger.
A fourth type of growth, actinic or solar keratosis, is also of concern because it can progress into cancer. It's the most common pre-malignant skin condition, occurring in more than 5 million Americans.
UV's Double Whammy
While there's no question that UV damages DNA, scientists had long suspected that it delivers a double whammy. Recent research supports that idea. Developing skin cancer is at least a two-step process, involving initiation and promotion of malignant growth. "UV plays both roles," says Douglas Brash, Ph.D., a biophysicist at Yale University School of Medicine. In studies with mice, Brash and colleagues showed that UV harms a mechanism for repairing cell damage. Once the repair system is impaired, cells become increasingly vulnerable to injury. Subsequent UV exposures just make matters worse, and can initiate malignancy.
After UV exposure, the repair mechanism normally directs damaged cells to commit suicide. That's why skin peels after a sunburn. "It's a mop-up operation," says Brash. But previously damaged cells with a malfunctioning repair system escape this mop up. Genetic damage accumulates as normal cells die and abnormal ones survive.
Brash said the level of UV used in their experiments was about equivalent to exposure from a day at the beach. Skin doesn't have to be badly sunburned, he said, adding that such damage also accumulates with chronic, everyday exposure.
To increase awareness of the damaging potential of UV radiation, the Environmental Protection Agency and the National Weather Service developed the UV Index. Besides skin cancer, UV radiation also increases the risk of cataracts and certain other eye problems, and can suppress the immune system. And although dark-skinned people are generally less likely to get skin cancer than light-skinned people, they are just as susceptible to cataracts or immune suppression.
The UV Index number, ranging from 0 to 10+, indicates the amount of UV radiation reaching the Earth's surface during an hour around noon. (See "UV or not Uv.") It's forecast daily for 58 cities, based on local predicted conditions. The UV Index is valid only for about a 30-mile radius from the city, and, as with any forecast, local variability in cloud cover and other factors may change actual levels experienced. But it serves as a reminder to take precautions against UV exposure.
For many people, sunscreens are the first line of defense.
"With most sunscreens it's important to apply them before you're in the sun," says FDA microbiologist Jeanne Rippete, who evaluates over-the-counter drugs, including sunscreens. They should be applied liberally, and reap-plied at least every two hours (more often if you're sweating) or after swimming or toweling off. Sunscreens are rated by an SPF (sun protective factor) number, which is a multiplier of your skin's exposure time before burning. For example, an SPF of 4 means you can stay in the sun four times longer before burning than if you were wearing no sunscreen. Keep in mind that you can't add SPF numbers. If an SPF 4 product gives you an hour in the sun, reapplying won't give you another hour. Your time's up. If you want longer exposure, next time use a higher SPF before going into the sun.
Something else to remember is that two types of UV radiation reach the Earth, UVA and UVB. Both contribute to skin damage, including skin cancer. There are no "safe" UV rays. But the SPF numbering system was devised as a guide to protect against sunburn, which is caused mostly by UVB. Because sunscreens allow you to stay out in the sun longer without burning, you may be increasing your exposure to UVA.
FDA has not approved a rating system for UVA protection because experts haven't reached a consensus as to what constitutes a good test. FDA is working to develop one, but until such a test exists, there's no way to compare products or verify claims made for UVA protection. Manufacturers are allowed to claim UVA or broad-spectrum protection on a product, as long as it contains an ingredient that absorbs UVA.
The American Academy of Dermatology recommends that everyone use a broad-spectrum sunscreen having an SPF of at least 15, and advises consumers to check for ingredients that screen UVA: benzophenone, oxybenzone, sulisobenzone, titanium dioxide, zinc oxide, and butyl methoxydibenzoyl-methane (also called avobenzone and known by the trade name Parsol 1789).
"People should not depend totally on sunscreens," Rippete says.
While sunscreens protect against sun-bum, they don't necessarily prevent cancer. If you use sunscreens to spend more time in the sun, your skin could collect about the same total exposure to damaging radiation. So it's still a good idea to stay out of the sun at midday, and to protect yourself with a wide-brim hat and clothing.
Wear Some Shade
Clothing offers the advantages of even, non-sticky protection that you don't have to remember to reapply. But many summer-weight fabrics don't give enough protection. Some are well below the minimum SPF 15 that dermatologists recommend. And fibers like cotton offer even less protection when wet.
"You can't just put on any old shirt and expect it to protect you," says Julian Menter, Ph.D., research professor of medicine at Morehouse School of Medicine in Atlanta, Ga. "Fabrics can differ greatly in their ability to shield you from UV radiation."
The ideal sun protective fabrics are lightweight, comfortable, and protect against exposure even when wet. Clothing that is labeled or promoted as providing protection against the sun or limiting exposure to UV rays is considered a medical device and is regulated by FDA. Sun Precautions, Inc., of Seattle, Wash., has received FDA clearance to market its Solumbra clothing for sun protection and is allowed to claim an SPF of 30 for its products.
In an experiment with mice, Menter and colleagues compared a so-called "typical" summer clothing fabric (a tightly woven cotton used in a gardening shirt) with the Solumbra fabric, a proprietary, tightly woven synthetic. With an SPF of 6.5, the cotton fabric protected mice against short-term UV effects, but it didn't protect against long-term skin damage, including skin cancel In fact, the incidence of tumors in these mice was comparable to that of the mice who received no UV protection. Mice not subjected to any UV radiation and the mice protected by the Solumbra fabric showed no signs of skin damage.
How do fabrics block UV? "It's a combination of factors--fabric thickness, composition of the fiber itself, and especially tightness of weave," says Deborah F. Lumbardo, an FDA biomedical engineer. Dye can be a factor too, she says.
"But remember that you still need to be using sunscreen on whatever areas are exposed," Lumbardo says.
Some studies estimate that diet may be involved in 40 to 60 percent of all cancers. More specifically, a high-fat diet has been implicated in colon and breast cancers. In animal studies, a high fat intake increased the likelihood of skin cancer after exposure to UV radiation, while switching to a low-fat diet after exposure reduced the incidence of skin cancer.
Homer S. Black, Ph.D., a researcher at the Veterans Affairs Medical Center in Houston, and his colleagues found a dietary effect in humans as well. In their study, published in the New England Journal of Medicine, a low-fat diet decreased the incidence of actinic keratosis in non-melanoma skin cancer patients. "The risk factors for actinic keratosis and non-melanoma skin cancer are basically the same," says Black.
The high-fat group ate their usual diet, consuming 36 to 40 percent of their caloric intake as fat, about average for Americans. In the low-fat group, no more than 20 percent of total caloric intake was fat. Overall, the high-fat group had a nearly five times greater risk of developing one or more actinic keratoses during the two-year study.
"Reduced incidence of this common skin tumor is just another added benefit to a long litany of those that can be attributed to a low-fat diet," Black says.
The National Academy of Sciences recommends a diet in which 30 percent or less of calories come from fat. The National Cancer Institute, the American Cancer Society, the American Heart Association, and other health organizations support this recommendation.
Although many researchers are studying the effects of certain vitamins and various other nutrients on skin cancer, it's too soon to make specific recommendations. But so far, the research trends point toward what we already know to be a healthier diet--less fat, more fruits, vegetables and grains.
Once cancer develops, early detection and treatment are the best defense. Get familiar with your skin and your own pattern of moles and freckles with monthly skin self-exams. If any growth, mole or discoloration appears suddenly or begins to change, or if a sore appears that doesn't heal, see a dermatologist.
For any type of skin cancer, treatment involves removing the lesion, usually in an outpatient procedure. The treatment goal is to remove or destroy the growth completely with as little damage as possible to healthy tissue. Doctors evaluate numerous factors in planning treatment. Considerations include type of cancer, tumor size and location, extent of disease, whether it's new or recurrent, potential for scarring, and the patient's overall health.
Types of surgery include cryosurgery (destruction by freezing), laser surgery (using a laser beam to cut away or vaporize growths), and curettage and electrodessication (using a spoon-like blade to scoop out the growth, followed by destruction of surrounding tissue with an electric needle). Occasionally, other treatments, such as radiation therapy or chemotherapy, may be used alone or in combination.
Even after successful treatment, people who have had skin cancer remain at increased risk of developing it again. Protecting their skin from UV exposure is critical in helping to prevent a recurrence. It should become a life-long habit. .
Weather Service UV Index
UV Index Exposure
0 - 2 minimal
3 - 4 low
5 - 6 moderate
7 - 8 high
9 - 10+ very high
TEST YOUR RISK FROM UV RADIATION
Your risk of skin cancer is related to your skin type and the amount of time you spend in the sun. How sensitive are you?
* I have blond or red hair [ ] [ ]
* I have light-colored eyes (blue, gray, green) [ ] [ ]
* I freckle easily [ ] [ ]
* I have many moles [ ] [ ]
* I had two or more blistering sunburns as
a child [ ] [ ]
* I spent lots of time in a tropical climate
as a child [ ] [ ]
* There is a family history of skin cancer [ ] [ ]
* I spend a lot of time in outdoor activities [ ] [ ]
* I like to spend as much time in the sun
as I can [ ] [ ]
* Score 10 points for each "YES"
* Add another 10 points if you go to tanning parlors or use a sun lamp
(Test courtesy of Dr. Neil Shear, University of Toronto)
80-110: The high-risk zone. Limit you time in the sun, always wear a sunscreen outdoors, and use protective clothing and a hat.
40-70: Increased risk. Use a sunscreen and hat regularly. Avoid exposure at midday when the sun is most intense.
10-30: Still at risk. Use a sunscreen regularly.
By Carolyn J. Strange
Carolyn J. Strange is a science writer in Saratoga, Calif