Population-based matched cohort study of the effect of pre-existing dementia on cancer-specific and all-cause mortality of cancer patients in Denmark

As the global population ages, the prevalence of both cancer and dementia increases. A population-based matched cohort study in Denmark investigated the effect of pre-existing dementia on cancer-specific and all-cause mortality in patients diagnosed with cancer. The study enrolled 17,425 patients with cancer and dementia diagnosed before the cancer diagnosis between 1995 and 2022, matched 1:5 by cancer site, age, sex, and calender period to cancer patients without comorbid dementia (n=86,823). Patients with cancer and comorbid dementia had a 5-year cancer-specific mortality rate of 44.0% (95% CI 43.2-44.7), compared with 39.4% (39.1-39.8) among patients with cancer without comorbid dementia. Excess cancer-specific mortality associated with dementia was highest among patients with colon cancer (risk difference 13.8%), rectal cancer (!4.8%), and breast cancer (8.9%). Comparison of patients with cancer and comorbid dementia versus patients with cancer alone revealed high 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. The authors conclude that clinical guideline for cancer screening and treatment in individuals living with dementia should be developed.