Marathon Training Runs Up Risk of Melanoma

GRAZ, Austria, Nov. 20 -- Training for the marathon puts runners at risk for malignant melanoma and other skin cancers, according to researchers here.

A study of 210 runners recruited from a local marathon, compared with 210 matched controls recruited from a skin cancer screening campaign, showed significantly more atypical moles (47.1% versus 31.4%, P=0.001) and numerous "liver spots" (30.5% versus 20.0%, P=0.01) indicating a greater risk for malignant melanoma.

The runners had significantly more signs of non-melanoma skin cancer compared with age- and sex-matched controls, reported Christina M. Ambros-Rudolph, M.D., Medical University of Graz, and colleagues, in the November issue of the Archives of Dermatology.

Dr. Ambros-Rudolph and colleagues referred almost twice as many marathon runners as controls (24 versus 14) to local dermatologists for surgical treatment of skin lesions suggestive of non-melanoma skin cancer, including basal cell carcinomas, squamous cell carcinomas, and actinic keratoses.

The referral rate was highest among runners who trained most (19.4% more than 70 km/week, 12.9% 40 to 70 km/week, and 6.4% less than 40 km/week).

Along with the control participants, the runners (median age 37, range 19 to 71) completed a comprehensive questionnaire on risk factors for the development of melanoma including personal and family history of skin cancer, changes in skin lesions, hair color, eye color, number of freckles, sun sensitivity, and number of sunburns with and without blisters. All participants also had a total body skin examination by a dermatologist.

Most marathon runners in the study ran less than 40 km per week (37.1%) or 40 to 70 km per week (48.1%), risk factors were particularly pronounced among runners who trained most. They reported:

• Among runners who trained less than 40 km per week, 41.0% had at least one atypical mole and 29.5% had numerous liver spots.
• Among athletes who ran 40 to 70 km per week, 50.5% had at least one atypical mole and 27.7% had numerous solar lentigines.
• Among runners who trained more than 70 km per week, 51.6% had at least one atypical melanocytic nevus and 41.9% had numerous moles.

This was despite higher sun sensitivity in the control group as reflected by more individuals with blue, green, or gray eye color and Fitzpatrick skin type I or II. The control group also more frequently had at least 50 common moles (22.4% versus 13.8%, P=0.03).

Neither group had any skin lesions suggestive of malignant melanoma diagnosed on clinical examination.

The runners reported typically wearing running shorts (96.7%) and short sleeve (87.6%) or sleeveless (11.0%) shirts, leaving most of their skin exposed to ultraviolet radiation for long periods. Only 56.2% reported regular use of sunscreen during exercising while 41.9% reported occasional use and 1.9% reported none.

In addition to UV radiation from sunlight, marathon runners may also experience repeated immunosuppression from excessive endurance exercise that favors development of skin cancer, the researchers theorized.

"Although regular low-impact exercise is well established to improve one's health," they wrote, "overtraining, high-intensity training, and excessive exercise, such as cumulative training for a marathon, the marathon itself, and, in particular, an ultramarathon, may lead to suppressed immune function."

The researchers, enthusiastic runners themselves, said the study was stimulated by the observation of eight ultramarathon runners (seven men and one woman; median age, 50 years; age range, 35-56; mean weekly training intensity, 120 km) with malignant melanoma over the past decade.

They suggested that clinicians counsel patients interested in marathon running to "reduce UV exposure during exercising by choosing training and competition schedules with low sun exposure, wearing adequate clothing, and regularly using water-resistant sunscreens."