title: Associations between cancer and Alzheimer's disease in a U.S. Medicare population.
abstract: Several studies have reported bidirectional inverse associations between cancer and Alzheimer's disease (AD). This study evaluates these relationships in a Medicare population. Using Surveillance, Epidemiology, and End Results (SEER) linked to Medicare data, 1992-2005, we evaluated cancer risks following AD in a case-control study of 836,947 cancer cases and 142,869 controls as well as AD risk after cancer in 742,809 cancer patients and a non-cancer group of 420,518. We applied unconditional logistic regression to estimate odds ratios (ORs) and Cox proportional hazards models to estimate hazards ratios (HRs). We also evaluated cancer in relation to automobile injuries as a negative control to explore potential study biases. In the case-control analysis, cancer cases were less likely to have a prior diagnosis of AD than controls (OR = 0.86; 95% CI = 0.81-0.92). Cancer cases were also less likely than controls to have prior injuries from automobile accidents to the same degree (OR = 0.83; 95% CI = 0.78-0.88). In the prospective cohort, there was a lower risk observed in cancer survivors, HR = 0.87 (95% CI = 0.84-0.90). In contrast, there was no association between cancer diagnosis and subsequent automobile accident injuries (HR = 1.03; 95% CI = 0.98-1.07). That cancer risks were similarly reduced after both AD and automobile injuries suggest biases against detecting cancer in persons with unrelated medical conditions. The modestly lower AD risk in cancer survivors may reflect underdiagnosis of AD in those with a serious illness. This study does not support a relationship between cancer and AD.
authors.affiliation: Department of Health and Human Services, National Institutes of Health, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Maryland. freedmam@mail.nih.gov.
authors.forename: Daryl Michal
authors.initials: DM
authors.lastname: Freedman
authors.affiliation: Department of Health and Human Services, National Institutes of Health, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Maryland.
authors.forename: Jincao
authors.initials: J
authors.lastname: Wu
authors.affiliation: Aging and Neuro-epidemiology Group, National Institute of Environmental Health Sciences, Research Triangle Park, Durham, North Carolina.
authors.forename: Honglei
authors.initials: H
authors.lastname: Chen
authors.affiliation: Department of Biology, University of Redlands, Redlands, California.
authors.forename: Ralph W
authors.initials: RW
authors.lastname: Kuncl
authors.affiliation: Department of Health and Human Services, National Institutes of Health, Division of Cancer Control and Population Sciences, National Cancer Institute, Rockville, Maryland.
authors.forename: Lindsey R
authors.initials: LR
authors.lastname: Enewold
authors.affiliation: Department of Health and Human Services, National Institutes of Health, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Maryland.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Engels
authors.affiliation: Department of Health and Human Services, National Institutes of Health, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Maryland.
authors.forename: Neal D
authors.initials: ND
authors.lastname: Freedman
authors.affiliation: Department of Health and Human Services, National Institutes of Health, Division of Cancer Epidemiology and Genetics, National Cancer Institute, Rockville, Maryland.
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Pfeiffer
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000150:complications / Q000453:epidemiology*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D006278:Medicare; D009369:Neoplasms / Q000150:complications / Q000453:epidemiology*; D016017:Odds Ratio; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D018426:SEER Program; D014481:United States / Q000453:epidemiology
keywords: Alzheimer's disease; Cancer; case-control; cohort