Effect of a Dementia Diagnosis on Survival of Older Patients After a Diagnosis of Breast, Colon, or Prostate Cancer: Implications for Cancer Care

Abstract

Impairment in cognitive function may interfere with the diagnosis and treatment of older patients with cancer. Two previous studies have reported an association of preexisting dementia with later-stage diagnosis of cancer. Limited data are available on the association between comorbid dementia in patients newly diagnosed with cancer and deaths from cancer and noncancer causes. Such knowledge could affect treatment decisions. This retrospective cohort study evaluated the associations between preexisting diagnoses of dementia and survival from breast, colon, and prostate cancer among 106,061 patients aged 68 years or older. The study subjects were identified through Medicare claims linked to the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) tumor registry data. The comparison group was patients with cancer having no known diagnosis of dementia. For each type of cancer, a Cox model was used to assess the interaction between preexisting dementia diagnosis and cancer. Logistic regression models were used to adjust for confounding variables. Of the 106,061 study subjects, 31,935 patients had breast cancer, 26,891 had colon cancer, and 47,235 had prostate cancer. A diagnosis of dementia was made in 7% of the study sample. Compared with nondemented patients, demented patients with cancer were significantly less likely to survive and to be diagnosed at an early stage of cancer. The risk of noncancer deaths within 6 months of a diagnosis of cancer in demented patients was higher (33.3%) compared with patients without dementia (8.5%). Adjustment for cancer stage revealed that a more advanced cancer stage at diagnosis in patients with dementia could explain 16.4% and 13.6% of the increased all-cause mortality in breast and colorectal cancer, respectively, but none of the excess mortality in prostate cancer. Among patients diagnosed with dementia, the effect of stage at diagnosis for all 3 cancers on cancer-specific or all-cause mortality was markedly reduced. The lack of a relationship between cancer stage at diagnosis and survival in older patients diagnosed with dementia suggest to the investigators that cancer screening guidelines for nondementia populations may be inappropriate in this study population.