Patterns of staging, treatment, and mortality in gastric, colorectal, and lung cancer among older adults with and without preexisting dementia: a Japanese multicentre cohort study

BACKGROUND: Little is known about dementia’s impact on patterns of diagnosis, treatment, and outcomes in cancer patients. This study aimed to elucidate the differences in cancer staging, treatment, and mortality in older cancer patients with and without preexisting dementia. METHODS: Using cancer registry data and administrative data from 30 hospitals in Japan, this multicentre retrospective cohort study examined patients aged 65–99 years who were newly diagnosed with gastric, colorectal, or lung cancer in 2014–2015. Dementia status (none, mild, and moderate-to-severe) at the time of cancer diagnosis was extracted from clinical summaries in administrative data, and set as the exposure of interest. We constructed multivariable logistic regression models to analyse cancer staging and treatment, and multivariable Cox regression models to analyse three-year survival. RESULTS: Among gastric (n = 6016), colorectal (n = 7257), and lung (n = 4502) cancer patients, 5.1%, 5.8%, and 6.4% had dementia, respectively. Patients with dementia were more likely to receive unstaged and advanced-stage cancer diagnoses; less likely to undergo tumour resection for stage I, II, and III gastric cancer and for stage I and II lung cancer; less likely to receive pharmacotherapy for stage III and IV lung cancer; more likely to undergo tumour resection for all-stage colorectal cancer; and more likely to die within three years of cancer diagnosis. The effects of moderate-to-severe dementia were greater than those of mild dementia, with the exception of tumour resection for colorectal cancer. CONCLUSION: Older cancer patients with preexisting dementia are less likely to receive standard cancer treatment and more likely to experience poorer outcomes. Clinicians should be aware of these risks, and would benefit from standardised guidelines to aid their decision-making in diagnosing and treating these patients. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12885-022-10411-y.