Skin cancer's return: how big a threat?

People who have already suffered one bout with certain skin cancers are risk of getting the disease again. A new study quantifies that menace and provides dermatologists with a more detailed picture of squamous and basal cell cancers, two very common and highly curable types of skin cancer.

Previous studies suggesting an increased risk of new tumors in patients treated for these nonmelanoma skin cancers were too small to provide definitive results. Now, Margaret R. Karagas and John A. Baron of Dartmouth Medical School in Hanover, N.H., and their colleagues report the results of the largest multicenter study of such skin cancers to date. Their research shows that people with a history of squamous and basal cell cancers run a 35 percent risk of developing another tumor within three years and a 50 percent risk within five years.

"It's the best study of its kind," comments dermatologist Howard Koh of Boston University School of Medicine. The findings indicate that the magnitude of the jeopardy for people with prior skin cancers is higher than previously suspected Koh adds.

The researchers studied 1,805 people with a history of nonmelanoma skin cancer. Unlike melanoma, an aggressive cancer that often spreads lethally beyond the skin, nonmelanoma skin cancers behave more indolently. Basal and squamous cell cancers can appear as pale, waxy nodes or red, scaly patches on the skin. If promptly treated, nonmelanoma skin cancers rarely cause death.

The study involved patients visiting clinical centers in Los Angeles, San Francisco, Minneapolis and Hanover. All volunteers were free of cancer at the study's start and had completed a questionnaire about their exposure to sunlight and personal characteristics such as skin type and hair color. All participants agreed to visit their dermatologists annually. The research team kept track of any new skin cancers that surfaced during a five-year follow-up period.

The researchers discovered that new skin cancers reported during follow-up tended to be the same cell types as the patient's previous tumor. However, the additional tumors were not caused by spread of the original cancer, the researchers note.

The risk of a subsequent cancer was higher for men, for people age 60 and older, and for volunteers who had reported many previous skin cancers. People who burn easily when exposed to the sun had a heightened risk of developing another nonmelanoma skin cancer.

Baron suspects that men may face an increased risk because they are more likely than women to work outdoors and thus to receive more exposure to skin-damaging ultraviolet rays. Jeopardy may intensify with age simply because years of exposure to the sun take a cumulative toll, he adds.

In an intriguing finding, the study revealed a link between cigarette smoking and the risk of squamous cell cancer. "It is conceivable that cigarette smoke acts directly as a skin carcinogen," the authors write in the June 24 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION. However, the association between smoking and skin cancer is preliminary, they note. At the same time, the researchers found no clear relationship between smoking and basal cell cancer.

Study participants who lived in Los Angeles and San Francisco ran a greater risk of developing another nonmelanoma skin cancer than did recruits who lived in Minneapolis and Hanover, the researchers discovered. They suggest that ongoing exposure to the sun may be to blame.

Koh and the researchers stress that limiting exposure to the sun is an important first step to prevention. "We think that a great deal of nonmelanoma skin cancer can be prevented with the proper sun precautions," he says. They advise everyone -- especially people with a history of skin cancer -- to wear strong sunscreen and protective clothing when outdoors. In addition, they recommend that peoples stay out of the sun at midday, when ultraviolet rays are strongest.