Planet UltraMarathon

November 28, 2006 — Marathon runners should wear adequate clothing and choose training times with low sun exposure to reduce the risk of developing malignant melanoma and nonmelanoma skin cancers, according to the results of a study reported in the November issue of the Archives of Dermatology.

"Marathon running has surged in popularity; it is generally believed to be healthy, but may be associated with medical risks," write Christina M. Ambros-Rudolph, MD, of the Medical University of Graz in Austria, and colleagues. "Over the past decade, we observed 8 ultramarathon runners with malignant melanoma. UV exposure, immunosuppression due to long term intensive exercise, or both have been discussed as potential triggers in these patients."

In this pilot case-control study, the investigators compared sun-related, clinical, and other variables in 210 marathon runners vs those of an age- and sex-matched control group.

The control group had higher sun sensitivity and more common melanocytic nevi, whereas marathon runners presented with more atypical melanocytic nevi, solar lentigines, and lesions suggestive of nonmelanoma skin cancer. In the marathon runners, these abnormalities correlated with increasing training intensity. During exercising, most runners wore shorts (96.7%) and shirts (98.6%) that would only partially cover their back and extremities, and only 56.2% of runners reported regular use of sunscreen.

"Compared with a representative control group, marathon runners presented with an increased risk for malignant melanoma and nonmelanoma skin cancer," the authors write. "Until further sport-physiologic studies elucidate in detail the potential association between exercise-induced immunosuppression and malignant melanoma, runners should be alerted to the crucial role of UV radiation in the development of malignant melanoma and non-melanoma skin cancer. In particular, they should be advised 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."

The authors have disclosed no relevant financial relationships.

Arch Dermatol. 2006;142:1471-1474.

Learning Objectives for This Educational Activity

Upon completion of this activity, participants will be able to:

• Describe the theoretical relationship between intense outdoor exercise and the risk for malignant melanoma.
• Compare skin findings among marathon runners vs an age- and sex-matched control group.

Clinical Context

Most patients believe exercise to be completely beneficial in terms of its health consequences, but the authors of the current study describe some theoretical reasons why athletes who train intensely in sunlight may be at an increased risk for malignant melanoma. The current authors focus particularly on athletes who train for and participate in marathons, noting that the average training time per event easily exceeds the recommended exposure to UV radiation. Moreover, sweating can increase the photosensitivity of skin, and most athletes do not wear clothing designed to protect sensitive areas along the upper back and lower legs. Finally, athletes who push their bodies physically can reduce their cell-mediated immune response, an established risk factor for malignant melanoma.

The researchers of the current study compare complete skin examinations among marathon runners and a control group of age- and sex-matched adults.

Study Highlights

• The study compared data from a cohort of marathon runners vs a group of adults who volunteered for skin cancer screening in 1 of 5 recreation centers in Austria. All subjects were white.
• Demographic and phenotypic data were collected along with a personal and family history of dermatologic conditions. Lifetime sun exposure and degree of sun burning was assessed, and all subjects underwent a total body skin examination.
• The main study outcome was the incidence of skin lesions discovered in the marathon vs control groups. The authors also related the intensity of marathon training to this outcome.
• 420 subjects in the marathon and control groups formed the research cohort. The median age was 37 years, and 79% of participants were men.
• Control subjects had higher degrees of sun sensitivity vs the marathon group, as reflected by more participants with blue, green, or gray eye color and lighter skin. Participants in the control group also had higher rates of common melanocytic nevi.
• Rates of diagnosis of at least 2 atypical melanocytic nevi were 47.1% and 31.4% of the marathon and control groups, respectively, a significant difference. Rates of solar lentigines were higher in the marathon vs control groups.
• No lesions suggestive of malignant melanoma were found on any study participant.
• 24 subjects in the marathon group were referred for surgical treatment of skin lesions compared with only 14 subjects in the control group.
• Higher training intensity within the marathon group predicted a higher rate of atypical nevi and referral for skin surgery.
• Among the marathon group, rates of training in shorts were 96.7%, and 98.6% of participants ran in short-sleeved or sleeveless shirts. 56.2% of subjects in the marathon group reported using sunscreen on a regular basis.

Pearls for Practice

• Marathon runners may have an increased risk for malignant melanoma compared with other individuals due to increased exposure to UV radiation, increased photosensitivity of the skin due to sweat, inadequate clothing to protect against UV radiation, and suppression of cell-mediated immunity.
• In the current study, marathon runners were more likely than the control group to have atypical melanocytic nevi and solar lentigines. Runners were also more likely to be referred for surgical treatment of skin lesions.