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.

重要性 窄带UV-B（NBUVB）光疗一直是治疗白癜风的主要方法，但尚未确定其在光致癌性方面的长期安全性。

目的 根据NBUVB光疗疗程的次数，调查接受NBUVB光疗的白癜风患者皮肤癌和癌前病变的风险。

设计，背景和参与者 这项基于全国人群的回顾性队列研究纳入了2007年1月1日至2017年12月31日之间60321名20岁或20岁以上的白癜风患者。患者和结局是通过韩国国民健康系统的全国队列数据确定的保险理赔数据库，并按年龄和性别进行频率匹配。

暴露 2008年至2017年期间，每位患者接受的光疗次数。根据光疗次数将患者分为5组（0次，20 105例； 1-49次，20 106例； 50-99次，9702例） ； 100-199次疗程，6226例患者；≥200疗程，4182例）。我们还确定接受至少500次光疗的患者（717例患者）。

主要结果和指标 初步结果是入选后发生光化性角化病，博文病，非黑色素瘤皮肤癌或黑色素瘤。

结果 接受过200次以上NBUVB光疗的患者，光化性角化病的风险显着增加（HR，2.269 [95％CI，1.530-3.365]）。总计717名白癜风患者接受了至少500次NBUVB光疗；非黑素瘤皮肤癌和黑色素瘤的风险不大于未进行NBUVB光疗的患者（非黑素瘤皮肤癌：HR，0.563 [95％CI，0.076-4.142]；黑素瘤：HR，不适用）。HR，0.563 [95％CI，0.076-4.142]；黑色素瘤：HR，不适用）。HR，0.563 [95％CI，0.076-4.142]；黑色素瘤：HR，不适用）。

结论与相关性 我们的结果表明，长期使用NBUVB光疗不会增加白癜风患者患皮肤癌的风险，因此NBUVB光疗可能被认为是一种安全的治疗方法。