In the era of biologic therapy, phototherapy and methotrexate (MTX) are still commonly used for treatment in patients with moderate-to-severe psoriasis. However, the skin cancer risk following a combination of MTX and narrowband ultraviolet B (NB-UVB) has rarely been explored.

To investigate whether MTX plus NB-UVB increases skin cancer risk in patients with psoriasis.

We conducted a retrospective cohort study of data in the Taiwan National Health Insurance Research Database from 1997 to 2013. Cumulative incidences and multivariate analysis were investigated using a competing risk regression model, comparing skin cancer risk between cohorts of people having combination therapy and those using NB-UVB alone, matched for relative confounders. We further conducted a sensitivity analysis for those receiving a higher MTX dose. Standardized incidence ratios (SIRs) were calculated for skin cancer risk.

We enrolled 3203 participants in each cohort. No significant differences in skin cancers were noted between the two cohorts for the cumulative incidences (log-rank test, P = 0.28) and for the hazard ratio (HRs) [adjusted HR 0.50, 95% confidence interval (CI) 0.15-1.63, P = 0.247] in the competing risk regression model. There were also no significant differences between those receiving higher-dose MTX and UVB alone in the cumulative incidences of skin cancers (P = 0.23) and the HR (adjusted HR = 0.29, 95% CI 0.04-2.21, P = 0.23) in the multivariate analysis. There was no significant difference in the SIR between the two cohorts compared with the general population.

In the Taiwanese population, MTX does not increase skin cancer risk in patients with moderate-to-severe psoriasis receiving NB-UVB.