The more abnormally shaped moles you have, the greater your risk of the deadly skin cancer melanoma, according to a study published in today’s issue of the Journal of the American Medical Association.
For more than 20 years, some doctors have observed that many people who develop melanoma also have flat, irregularly shaped moles with indistinct borders and variable pigmentation - called dysplastic nevi. But how much of a role these moles play in melanoma has been controversial, partly because the definition of dysplastic nevi has been imprecise and studies have been small, experts say.
Melanoma is the most serious skin cancer, with 40,300 new cases and 7,300 deaths expected this year. The incidence has been rising about 4 percent each year since 1973, according to the American Cancer Society, for reasons that are unclear but may have to do with increased sun exposure.
In the largest study to date, researchers at the National Cancer Institute examined 716 melanoma patients and 1,014 people matched by age, sex, race and area of the United States who did not have skin cancer. They found that having one dysplastic nevi - defined in the study as 5 millimeters or larger, the size of a pencil head - was associated with a two-fold risk of melanoma, and that having 10 or more dysplastic nevi was associated with a 12-fold risk of the cancer.
Those who are 50 and older and have many abnormal nevi are at even higher risk because most people stop developing or lose moles by that age. “… The point is that individuals over 50 with persistent dysplastic nevi (are) in a very high-risk group,” said Dr. Margaret Tucker, the lead researcher.
Those at high risk should “conservatively” be checked once a year, Tucker said, and perhaps have photographs taken to mark any changes.
Normally shaped moles - like fair skin and freckling - are also associated with an increased risk.