Importance: Narrowband UV-B (NBUVB) phototherapy has been the mainstay in the treatment of vitiligo, but its long-term safety in terms of photocarcinogenesis has not been established.

Objectives: To investigate the risks of skin cancer and precancerous lesions among patients with vitiligo undergoing NBUVB phototherapy, based on the number of NBUVB phototherapy sessions.

Design, setting, and participants: This nationwide population-based retrospective cohort study enrolled 60 321 patients with vitiligo 20 years or older between January 1, 2007, and December 31, 2017. Patients and outcomes were identified through nationwide cohort data from the Korean national health insurance claims database, and frequency matching by age and sex was performed.

Exposures: The number of phototherapy sessions each patient received between 2008 and 2017. Patients were classified into 5 groups according to the number of phototherapy sessions (0 sessions, 20 105 patients; 1-49 sessions, 20 106 patients; 50-99 sessions, 9702 patients; 100-199 sessions, 6226 patients; and ≥200 sessions, 4182 patients). We also identifed patients who underwent at least 500 phototherapy sessions (717 patients).

Main outcomes and measures: Primary outcomes were the development of actinic keratosis, Bowen disease, nonmelanoma skin cancer, or melanoma after enrollment.

Results: Among the 60 321 patients with vitiligo in this study (33 617 women; mean [SD] age, 50.2 [14.9] years), the risks of Bowen disease (<50 sessions of phototherapy: hazard ratio [HR], 0.289 [95% CI, 0.060-1.392]; 50-99 sessions: HR, 0.603 [95% CI, 0.125-2.904]; 100-199 sessions: HR, 1.273 [95% CI, 0.329-4.924]; ≥200 sessions: HR, 1.021 [95% CI, 0.212-4.919]), nonmelanoma skin cancer (<50 sessions: HR, 0.914 [95% CI, 0.533-1.567]; 50-99 sessions: HR, 0.765 [95% CI, 0.372-1.576]; 100-199 sessions: HR, 0.960 [95% CI, 0.453-2.034]; ≥200 sessions: HR, 0.905 [95% CI, 0.395-2.073]), and melanoma (<50 sessions: HR, 0.660 [95% CI, 0.286-1.526]; 50-99 sessions: HR, 0.907 [95% CI, 0.348-2.362]; 100-199 sessions: HR, 0.648 [95% CI, 0.186-2.255]; ≥200 sessions: HR, 0.539 [95% CI, 0.122-2.374]) did not increase after phototherapy. The risk of actinic keratosis increased significantly for those who had undergone 200 or more NBUVB phototherapy sessions (HR, 2.269 [95% CI, 1.530-3.365]). A total of 717 patients with vitiligo underwent at least 500 sessions of NBUVB phototherapy; their risks of nonmelanoma skin cancer and melanoma were no greater than those of the patients who did not undergo NBUVB phototherapy (nonmelanoma skin cancer: HR, 0.563 [95% CI, 0.076-4.142]; melanoma: HR, not applicable).

Conclusions and relevance: Our results suggest that long-term NBUVB phototherapy is not associated with an increased risk of skin cancer in patients with vitiligo and that NBUVB phototherapy may be considered a safe treatment.