The Association Between Cancer and Dementia: A National Cohort Study in Sweden

Abstract

Background: Previous studies have found that the incidence of dementia is lower in patients with cancer. However, the impact of survival bias, as well as the confounding by medical treatment, have not been fully addressed. We aimed to explore the subsequent risk of dementia in different follow-up intervals among patients with cancer, as well as the risk before the diagnosis of cancer.Methods: By using the Swedish Cancer Register and the Swedish Hospital Discharge Register, we systematically examined the risk of dementia among patients diagnosed with 35 different types of cancer. Standardized incidence ratios (SIRs) were used to calculate the relative risk. Results:The subsequent risk of dementia in patients with cancer decreased by 21% compared to matched cancer-free controls (SIR = 0.79, 95% CI 0.78-0.80). For specific cancer sites, 21 of them had a significantly lower risk of subsequent dementia. The decreased risk of dementia was also significant before the diagnosis of cancer. However, the risk was higher among patients with cancer who survived for more than 10 years' post-diagnosis (SIR = 1.37, 95% CI 1.32-1.41). Conclusions:In this population-based study, we found that the risk of dementia was lower among patients with cancer, and the risk was also lower before the diagnosis of cancer. This suggests that lower dementia risk is not simply due to bias. However, the underlying mechanisms need to be explored further.

Association Between Alzheimer Disease and Cancer With Evaluation of Study Biases

“…Our search returned 2764 unique records; 22 studies (19 cohort studies and 3 case-control studies) met the eligibility criteria and were included (eFigure 1 in the Supplement ). In total, 13 studies 10 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 investigated all cancer types (eTable 2 in the Supplement ); 5 studies 49 , 50 , 51 , 52 , 53 investigated prostate cancer; 3 studies 9 , 54 , 55 investigated NMSC; and 1 study 56 investigated breast cancer ( Table 1 ). Five studies that investigated all cancer types (5 of 13) additionally reported cancer type–specific subgroup analyses.…”

“…Three studies 41,42,46 included in this review presented time-varying HRs, but evidence from these reports is inconclusive.…”

“…Another strategy to address survival bias is to report HRs stratified by time since cancer diagnosis because bias from survival should increase with more time elapsed since cancer diagnosis. Three studies 41 , 42 , 46 included in this review presented time-varying HRs, but evidence from these reports is inconclusive.…”

Investigating the association between cancer and the risk of dementia: Results from the Memento cohort

“…Some limitations exist, most notable being the limited number of cancer cases, particularly of those diagnosed with both incident cancer and dementia (6.3%). Although this is indicative of the protective role that cancer appears to play in dementia risk, it impeded further investigations into the potential differential impact of specific cancer types on risk as well as a more sophisticate multi‐state model (ie, including incident cancer diagnosis as a separate state) 8,22,35,36 . Information on cancer stage was also not available; due to the influence of cancer stage on reductions in survival, stratification by cancer stage could have permitted a further in‐depth investigation into survival bias.…”

“…Although this is indicative of the protective role that cancer appears to play in dementia risk, it impeded further investigations into the potential differential impact of specific cancer types on risk as well as a more sophisticate multi‐state model (ie, including incident cancer diagnosis as a separate state). 8 , 22 , 35 , 36 Information on cancer stage was also not available; due to the influence of cancer stage on reductions in survival, stratification by cancer stage could have permitted a further in‐depth investigation into survival bias. However, in a national cohort study on US veterans, adjustment for cancer severity was not found to impact results in previous studies.…”