Dementia and cancer are 2 common diseases in the elderly. This retrospective cohort study used a population-based insurance claim dataset, merged with a cancer registry, to test whether risk reduction of cancers occurs at various primary sites after diagnosis of dementia. The study included a cohort of 3282 patients who were first diagnosed with dementia between 2001 and 2002. A control cohort consisted of 13,128 subjects matched for age, sex, and year of enrollment. The site of cancer and duration between the diagnosis of dementia and cancer were analyzed. Among the dementia cases, 169 patients (5.2%) were diagnosed with cancer during a median observation period of 40 months. In the control group, 976 subjects (7.4%) were diagnosed with cancer, during a median observation period of 46 months. During a 7-year follow-up period, the adjusted hazard ratio for cancer among dementia patients was 0.77 (95% confidence interval, 0.65-0.91), and significantly lower for colon (0.54, 0.29-0.99) and prostate cancers (0.44, 0.20-0.98). This study showed an inverse association between cancer and dementia. Further studies focusing on colon and prostate cancers may help elucidate the underlying mechanism and expand the therapeutic strategies.
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