Narrowband ultraviolet B (NB-UVB) phototherapy is a popular and relatively contemporary treatment option. However, only a few studies to date have explored the potential risk of skin cancer following NB-UVB treatment.

This study aimed to investigate the potential long-term risk of skin cancer in patients treated with NB-UVB.

This cohort study included patients with psoriasis, vitiligo, and mycosis fungoides treated with NB-UVB at two university hospitals in Israel in 2000-2005. Patients were followed up for skin cancer for at least 10 years. Data were extracted from the hospital and community medical records.

A total of 767 patients were included in this study: 509 with psoriasis, 122 with vitiligo, and 136 with mycosis fungoides. The mean follow-up duration was 13 years. Among these patients, 4.43% developed skin cancer during the follow-up (3.93% had psoriasis, 2.46% had vitiligo, and 8.09% had mycosis fungoides). Old age and fair skin type were the only significant independent risk factors for skin cancer. There was no significant difference in the mean number of NB-UVB treatments among patients who developed skin cancer and those who did not (99.09 vs. 94.79, respectively).

No association was observed between the number of NB-UVB treatments and carcinogenesis in any study group. Age is a significant risk factor, and older patients treated with NB-UVB should be followed up carefully.