Atopic dermatitis, venous thromboembolism and cancer: a cohort analysis.

Atopic dermatitis is a risk factor for venous thromboembolism which may be the first manifestation of occult cancer. We examined whether a venous thromboembolism in patients with atopic dermatitis is a marker of occult cancer. We used Danish health registries to conduct this population-based cohort study. Patients with a first-time diagnosis of venous thromboembolism and a history of atopic dermatitis were identified from the Danish National Patients Registry from 1980 through 2022. We calculated the absolute risk of cancer treating death as a competing event. As a measure of relative risk, we calculated standardized incidence ratios (SIRs) for cancer among patients with venous thromboembolism and atopic dermatitis and compared the observed cancer incidence to that of the general Danish population. We identified 582 patients with a first venous thromboembolism diagnosis and a history of atopic dermatitis. During the first year of follow-up, the absolute risk of overall cancer was 1.7%, corresponding to an SIR of 2.90 (95% confidence interval [CI] 1.39-5.34). The overall SIR decreased to 1.12 (95% CI 0.74-1.62) during the subsequent years of follow-up. Although the risk estimates were imprecise, an elevated cancer risk following venous thromboembolism in patients with atopic dermatitis cannot be ruled out, particularly within the first year after venous thromboembolism, when compared to the cancer risk in the general population.