Venous Thromboembolism and Risk of Cancer in Patients with Dementia: A Danish Population-Based Cohort Study.

BACKGROUND Venous thromboembolism (VTE) may be the first manifestation of occult cancer. Dementia has been linked to reduced cancer risk. OBJECTIVE We examined the risk of cancer following VTE in people with dementia in comparison to the risk in the general population. METHODS We conducted a population-based Danish registry-based cohort study following patients with a first-time VTE and a previous or concurrent diagnosis of dementia during the period 1 April 1996 -31 December 2017. We followed the study participants from date of VTE until diagnosis of cancer, death, emigration, or end of study period, whichever came first. The absolute risk of cancer within one year after VTE was computed, treating death as a competing risk. We calculated gender, age, and calendar-period standardized incidence ratios (SIRs) of cancer based on national cancer rates. RESULTS We followed 3,552 people with dementia and VTE for a median of 1.3 years. Within the first year after VTE, they had a 90% increased risk of cancer in comparison with the general population [SIR: 1.9 (95% confidence interval: 1.6-2.4)]. During subsequent follow-up years, the SIR fell to 0.7 (95% confidence interval: 0.5-0.8). Findings for Alzheimer's disease and VTE were similar. CONCLUSION People with dementia have an increased risk of a cancer diagnosis during the first year following VTE, perhaps related to increased surveillance, and a lower risk thereafter. Overall risk is similar to that of the general population.