Risk of All-Cause Dementia, Alzheimer Disease, and Vascular Dementia in Breast Cancer Survivors: A Longitudinal Register-Based Study.

BACKGROUND AND OBJECTIVES: Now more than two-thirds of cancer survivors are aged 65 years or older, but evidence about their long-term health is thin. Cancer and its treatments have been linked to accelerated aging, so there is a concern that aging cancer survivors have an increased risk of age-related diseases, including dementia.

METHODS: We examined the risk of dementia among 5-year breast cancer survivors using a matched cohort study design. We included breast cancer survivors aged 50 years and older at diagnosis (n = 26,741) and cancer-free comparison participants (n = 249,540). Women eligible for inclusion in the study were those born 1935-1975 and registered in the Swedish Total Population Register between January 1, 1991, and December 31, 2015. We defined breast cancer survivors as women with an initial breast cancer diagnosis between 1991 and 2005 who survived 5 or more years after their first diagnosis. We assessed all-cause dementia, Alzheimer disease (AD), and vascular dementia (VaD) using International Classification of Diseases codes. Survival analyses were conducted using age-adjusted subdistribution hazard models accounting for competing risk of death.

RESULTS: We did not observe an association between breast cancer survivorship and risk of all-cause dementia, AD, or VaD. However, in models stratified by age at cancer diagnosis, women diagnosed with cancer after age 65 years had a higher risk of all-cause dementia (subdistribution hazard ratio [SHR] = 1.30, 95% CI 1.07-1.58), AD (SHR = 1.35, 95% CI 1.05-1.75), and VaD (SHR = 1.64, 95% CI 1.11-2.43) in models adjusted for age, education, and country of origin.

DISCUSSION: Older breast cancer survivors who survive cancer have a higher risk for dementia than their peers without a cancer diagnosis, in contrast to earlier studies showing that prevalent or incident cancer is associated with a lower risk of dementia. With the older adult population growing rapidly and because cancer and dementia are 2 of the most common and debilitating diseases among older adults, it is critical that we understand the link between the 2.