The competing risk of death and selective survival cannot fully explain the inverse cancer-dementia association

Alzheimers Dement. 2020 Dec;16(12):1696-1703. doi: 10.1002/alz.12168. Epub 2020 Sep 3.


Introduction: We evaluated whether competing risk of death or selective survival could explain the reported inverse association between cancer history and dementia incidence (incidence rate ratio [IRR] ≈ 0.62-0.85).

Methods: A multistate simulation model of a cancer- and dementia-free cohort of 65-year-olds was parameterized with real-world data (cancer and dementia incidence, mortality), assuming no effect of cancer on dementia (true IRR = 1.00). To introduce competing risk of death, cancer history increased mortality. To introduce selective survival, we included a factor (prevalence ranging from 10% to 50%) that reduced cancer mortality and dementia incidence (IRRs ranged from 0.30 to 0.90). We calculated IRRs for cancer history on dementia incidence in the simulated cohorts.

Results: Competing risk of death yielded unbiased cancer-dementia IRRs. With selective survival, bias was small (IRRs = 0.89 to 0.99), even under extreme scenarios.

Discussion: The bias induced by selective survival in simulations was too small to explain the observed inverse cancer-dementia link, suggesting other mechanisms drive this association.

Keywords: Alzheimer's disease; cancer; competing risks; dementia; selection bias; simulation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Aged
  • Bias*
  • Cohort Studies
  • Computer Simulation*
  • Dementia* / epidemiology
  • Dementia* / mortality
  • Female
  • Humans
  • Incidence
  • Male
  • Neoplasms* / epidemiology
  • Neoplasms* / mortality
  • Prevalence
  • Risk Factors