The number and shape of moles on your skin may signal your risk of malignant melanoma, the most dangerous type of skin cancer. The findings, reported in tomorrow's issue of The Journal of the American Medical Association, suggest that doctors should routinely examine patients' moles during physical exams.
Although researchers have long known that large, irregularly shaped moles are the ones most likely to turn nasty, Margaret Tucker of the National Cancer Institute and her colleagues at Harvard Medical School wanted to pin down the relationship between size, number, and type of mole and melanoma risk. They asked dermatologists at two major skin cancer research centers--the Melanoma Clinic at the University of California, San Francisco, and the Pigmented Lesion Clinic of the Hospital of the University of Pennsylvania--to take detailed notes on the characteristics of patients' moles and which moles turned into melanoma.
After gathering data on 738 melanoma patients and 1030 nonmelanoma patients, Tucker's team found that subjects with more than 100 small moles--2 to 5 millimeters across--had twice as high a risk of melanoma as did people with fewer moles. In addition, having a single mole with an irregular outline or one mottled in color also doubled the risk. Patients with 10 or more irregular moles had 12 times the cancer risk of patients without such moles.
The results are not surprising, as other epidemiological studies have implicated moles as a risk factor for melanoma, says Sewa Legha, a clinical oncologist at the M. D. Anderson Cancer Center in Houston. However, he says, better quantifying the risk is important because too few doctors understand the importance of regular skin exams. "Physicians have not been well versed at recognizing abnormal moles," he says. "It should be a part of any routine physical exam." Tucker adds that her team's data "allow doctors to determine, based on physical exam, whether someone is at a moderate risk or a very high risk."