(38) Urticaria and Risk of Cancer: A Danish Population-Based Cohort Study

Publication Number: 1083

Background: Urticaria is a common sign of drug hypersensitivity, but recent case reports and limited studies suggest an association with occult cancer. The sparse epidemiological evidence is however conflicting.

Objectives: To examine the relative risk of cancer in people with urticaria.

Methods: Using Danish health registry data, we conducted a population-based cohort study of all individuals diagnosed with urticaria between 1980 and 2017. We followed them from urticaria diagnosis date until the first of: incident cancer diagnosis, death, emigration, or end of study (31 December 2018). We calculated cumulative incidence of cancer, treating death as a competing risk, and standardized incidence ratios (SIRs) as measures of relative cancer risk using Danish national cancer rates. In a sensitivity analysis, we investigated cancer risk in people with specific spontaneous urticaria diagnoses.

Results: We identified 71,942 individuals with urticaria (57% female) with a median follow-up time of 10.3 years (interquartile range: 4.5-18.7 years).
In the first year of follow-up, 482 people with urticaria were diagnosed with cancer, yielding an absolute cancer risk of 0.7% (95% confidence interval (CI): 0.6%-0.7%). The SIR for all cancers was 1.47 (95% CI: 1.34-1.61), with the highest SIRs for hematological cancers: Hodgkin’s lymphoma (SIR: 4.43, 95% CI: 1.78-9.12), non-Hodgkin’s lymphoma (SIR: 3.03, 95% CI: 2.06-4.30), lymphoid leukemia (SIR: 1.94, 95% CI: 0.84-3.82) and myeloid leukemia (SIR: 2.44, 95% CI: 0.89-5.31).
During subsequent follow-up, the overall cancer risk was only minimally increased, SIR: during 1 to < 10 years: 1.07 (95%: 1.03-1.11); 10 to < 20 years: 1.06 (95% CI: 1.01-1.11); and more than 20 years: 1.11 (95% CI: 1.05-1.18).
Cancer risk was elevated in people with spontaneous urticaria during the first year of follow-up (SIR: 1.28, 95% CI: 1.04-1.57) but was similar to that in the general population during the subsequent years.

Conclusions: Our study found that urticaria diagnosis was associated with an elevated short-term cancer risk. Long-term cancer risk remained slightly increased. This finding may reflect reverse causation but we cannot rule out the possibility of detection bias. Diagnostic testing beyond already recommended procedures for people with urticaria would probably not be cost-effective.