White marathon runners are at significantly higher risk of developing malignant melanoma than are white people of the same age who don't spend 40 or more hours per week training or competing outdoors, reported Dr. Christina M. Ambros-Rudolph and her associates at the Medical University of Graz (Austria).
Compared with an age-, sex-, and race-matched control population, marathon runners were found to have significantly more atypical melanocytic nevi and solar lentigines. Their referral rate for removal of lesions suggestive of nonmelanoma skin cancer also was significantly higher than that of control subjects.
Both the number of lesions and the rate of referral for surgical excision increased as the number of hours spent training outdoors increased, the researchers said (Arch. Dermatol. 2006;142:1471–4).
Physicians should alert patients who are runners to “the crucial role of UV radiation in the development of malignant melanoma and nonmalignant skin cancers. 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,” Dr. Ambros-Rudolph and her associates said.
They became concerned about malignant melanoma incidence among runners when they observed eight cases of the disease in marathoners treated in their dermatology department over the past decade. The researchers are themselves “enthusiastic runners,” and two are regular marathoners, they noted.
In all eight cases, melanomas developed in areas that were uncovered or only partially covered by clothing—the upper back, lower thigh, and calf—and all but one were associated with an atypical or congenital melanocytic nevus.
To study the issue, the investigators assessed 210 white marathon runners (166 men and 44 women) aged 19–71 years and 210 white age- and sex-matched control subjects for personal and family history of skin cancer, phenotypic markers, sunburn history, and training habits. All subjects underwent a total body skin examination.
Most runners reported that they trained and competed wearing shorts that left the legs uncovered and shirts that left the arms and upper back uncovered or only partially covered. Only about half said they regularly used sunscreen.
Control subjects showed higher sun sensitivity than did runners, with more cases of light eye color and of Fitzpatrick skin types I or II. Control subjects also had more melanocytic nevi. The runners, however, were found to have significantly more atypical nevi and solar lentigines, Dr. Ambros-Rudolph and her associates said.
Runners also were significantly more likely to be referred for surgical removal of suspicious lesions, including basal cell carcinomas, squamous cell carcinomas, and actinic keratoses.
The number of atypical nevi, solar lentigines, and suspicious lesions was highest in the runners who spent the most time training outdoors, they reported.
Exercise-induced immunosuppression commonly seen in endurance athletes may contribute to the higher risk of malignant melanoma in marathon runners, the researchers said.
In addition, professional athletes in other outdoor sports have been shown to receive over 30 times the daily limit of UV exposure recommended by the International Commission on Non-Ionizing Radiation Protection and the American Conference of Governmental Industrial Hygienists. Moreover, sweating during exercise has been shown to increase the photosensitivity of the skin, presumably via hydration of the horny layer and shifting in the stratum corneum UV absorption spectrum, Dr. Ambros-Rudolph and her associates noted.