Associations Between Prostate Cancer and Dementia: A Nationwide Study in Sweden.

Background and objective: Prostate cancer (PC) and dementia may commonly co-occur; yet, prior evidence for bidirectional associations is inconsistent. This study aims to determine the associations between PC and dementia in large population-based studies, which may further inform clinical care.

Methods: To assess the dementia risk in men with PC, a national cohort study was conducted in 178 746 men diagnosed with PC in 1998-2017 and 1 787 460 age-matched control men in Sweden without prior dementia. Cox regression was used to estimate hazard ratios (HRs) for Alzheimer's disease (AD) and vascular dementia (VaD) through 2018. Subanalyses explored differences by PC treatment during 2005-2017. To assess the PC risk in men with dementia, case-control analyses were performed in 180 189 men with PC and 1 801 890 age-matched control men. Logistic regression was used to estimate odds ratios (ORs) for PC associated with prior AD or VaD. All analyses were adjusted for sociodemographic factors and health care utilization.

Results and limitations: Among men with high-risk PC, those treated with androgen deprivation therapy (ADT) only had a higher risk of AD (HR, 1.37; 95% confidence interval [CI], 1.19-1.58) and VaD (1.51; 1.29-1.78), but not those who received other treatments. Men with low- or intermediate-risk PC had little or no increased risk of AD (HR, 1.10; 95% CI, 1.03-1.18) or VaD (0.90; 0.83-0.98). Men with AD or VaD had lower odds of high-risk PC (OR, 0.39; 95% CI, 0.35-0.45, and 0.36; 0.30-0.42, respectively) and low- or intermediate-risk PC (0.30; 0.25-0.36, and 0.30; 0.24-0.38, respectively). This study was limited to Sweden and will need replication when feasible.

Conclusions: In a large national study, men with high-risk PC treated with ADT had higher risks of AD and VaD. Such men should be monitored for timely detection and treatment of dementia. In contrast, men with AD or VaD had a lower subsequent risk of PC, possibly reflecting reduced screening in these subgroups.