Both Alzheimer’s disease (AD) and Parkinson’s disease (PD) are associated with lower cancer risk. However, the cancer risk in Parkinson’s disease dementia (PDD) has never been discussed. We aimed to test whether PDD is cancer protective, and to compare the types and risks of incident cancer between AD and PDD.
We used Taiwan National Health Insurance Database. From 1997 to 2010, a total of 2,527 PD dementia and 25,557 AD patients were enrolled and followed up for cancer by record linkage. Age and sex standardized incidence ratios (SIRs) of overall and site-specific cancers were calculated. Cox proportional hazards model was used to compare the cancer risk of AD relative to PDD.
With an average 4.4 years of follow-up period, both AD and PDD were associated with lower overall cancer risk (SIR and 95% confidence interval (CI): 0.83 (0.77-0.89) and 0.70 (0.55-0.89), respectively). The adjusted overall cancer risk of AD was significantly higher than that of PDD (hazard ratio (HR) and 95% CI: 1.26 (1.04-2.53), p=0.02). As for the site-specific cancer risk, the colorectal cancer risk of AD was also significantly higher than that of PDD (SIR: 0.95 (0.80-1.12) and 0.53 (0.80-1.00); HR: 1.83 (1.07-3.14), p=0.029).
Both AD and PDD are inversely associated with incident cancer. Compared to AD, PDD is associated with even lower cancer risk. The decreased cancer risk in PDD may be contributed by the combined effect from both AD and PD. The mechanism deserves further investigations.