There have been several reports of dupilumab use and the development of CTCL; however, the risk of CTCL development has not been adequately evaluated at the population level. The objective of this study is to determine whether dupilumab administration for AD is associated with an increased risk of developing CTCL and to identify at‐risk populations within this group. This retrospective cohort study used TriNetX, a deidentified medical record database including over 107 million patients, to identify eligible patients. Treatment and control groups were evaluated for the development of CTCL. Patients of any age with a documented diagnosis of AD were included. The treatment cohort included individuals treated with dupilumab, while the control cohort included AD patients treated with alternative therapies. Selected biologics were excluded from both groups. Subgroup analyses were performed to evaluate three age groups and to identify whether the risk of CTCL development was higher within a given time frame after starting dupilumab. We identified a total of 1,181,533 patients with AD. Of these, 19,612 patients were prescribed dupilumab. Both treatment and control groups included 19,612 patients matched for age, race, and sex. The mean age was 32.3 years (P = 0.96), and females accounted for approximately 52% (P = 0.93) in both groups. Patients treated with dupilumab for AD had an increased relative risk (RR) of developing CTCL compared to those never treated with dupilumab (RR = 4.59, 95% confidence interval 2.459–8.567, P < 0.0001). Subgroup analysis revealed that about half of the CTCL cases after dupilumab therapy (54.5%, 30/55) occurred in patients over the age of 60 years. In contrast, all CTCL cases (100%, 12/12) within the untreated cohort were observed in individuals over the age of 60. Of the patients diagnosed with CTCL following dupilumab use, the majority (62%, 34/55) were diagnosed within the first year. Overall, we find that the use of dupilumab for treating AD is associated with an increased relative risk of developing CTCL. This risk is highest in the first year of therapy and in adult patients. These findings suggest exercising caution in treating select groups of patients with dupilumab.
