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.