Effect of pre-existing dementia on cancer-specific and all-cause mortality in patients with cancer in Denmark: a population-based cohort study.

Authors

Lindsay J Collin, Holly C Elser, Dóra Körmendiné Farkas, Victor W Henderson, Erzsébet Horváth-Puhó, Henrik Toft Sørensen

Published in

The lancet. Healthy longevity. Pages 100908. Sep 29, 2026. Epub Sep 29, 2026.

Abstract

As the global population ages, the prevalence of both cancer and dementia continues to increase. We aimed to assess the effect of pre-existing dementia on cancer-specific and all-cause mortality among individuals diagnosed with cancer.
We conducted a population-based matched cohort study of Danish citizens using data from Danish health and administrative registries. We included all individuals diagnosed with cancer in Denmark between Jan 1, 1995, and Dec 31, 2022 and identified dementia diagnoses recorded before their cancer diagnosis. Individuals were excluded if they had an invalid civil personal registration number, did not have a Danish address before their cancer diagnosis, or had a cancer diagnosis recorded after death or emigration. Patients with cancer without comorbid dementia were randomly selected with replacement from the cohort and matched to patients with cancer and comorbid dementia by cancer site, age, sex, and calendar period, in a 5:1 ratio. We estimated 5-year mortality risk, risk differences (RDs), and multivariable-adjusted hazard ratios (HRs) with 95% CIs for the association between comorbid dementia and cancer-specific and all-cause mortality, overall and across key patient and cancer characteristics.
We identified 17 425 patients with cancer and comorbid dementia and 86 823 patients with cancer without comorbid dementia. Patients with cancer and comorbid dementia had a 5-year cancer-specific mortality of 44·0% (95% CI 43·2-44·7) compared with 39·4% (39·1-39·8) among patients with cancer without comorbid dementia (RD 4·5%, 95% CI 3·7-5·4), and an excess 5-year all-cause mortality (22·2%, 21·5-22·9). Excess cancer-specific mortality associated with dementia was the highest among patients with colon cancer (RD 13·8%, 95% CI 10·8-16·7), rectal cancer (RD 14·8%, 95% CI 10.3-19.2), and breast cancer (RD 8·9%, 95% CI 6·3-11·5%). Comparison of patients with cancer and comorbid dementia with patients those with cancer alone revealed higher cancer-specific mortality (multivariable-adjusted HR 1·28, 95% CI 1·24-1·31) and all-cause mortality (2·03, 1·98-2·07) among patients with cancer and dementia.
Cancer-specific and all-cause mortality rates were elevated among individuals with cancer and dementia. As treatments continue to improve survival outcomes for people with cancer and dementia, clinical guidelines for cancer screening and treatment in individuals living with dementia should be developed.
National Institutes of Health, Aarhus University.

PMID:
42810378
Bibliographic data and abstract were imported from PubMed on 30 Sep 2026.

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