The impact of environmental ultraviolet exposure on the clinical course of mycosis fungoides.

BACKGROUND: As phototherapy plays an important role in the treatment of early-stage mycosis fungoides (MF), it is possible that environmental ultraviolet (UV) exposure affects the natural history of the disease. OBJECTIVE: To assess the impact of environmental UV exposure on the clinical course of MF. METHODS: The National Solar Radiation Database was used to identify the top and bottom registries for UV exposure from the Surveillance, Epidemiology, and End Results-18 database. Incidence and survival were determined. RESULTS: The high-UV cohort had a 30% lower risk of developing MF than did the low-UV cohort (hazard ratio, 1.3; 95% confidence interval, 1.20-1.41; P < .001). When stratified by stage and race, this difference was appreciable only among those with early-stage disease and white race. There was no difference in survival between the high- and low-UV cohorts (P = .098); however, a small difference was observed among those with early-stage disease and white race, favoring high UV exposure. LIMITATIONS: Retrospective design, use of the National Solar Radiation Database as a surrogate for individual sunlight exposure. CONCLUSION: It is possible that environmental solar UV exposure may play a role in controlling early-stage MF among patients with photosensitive features.