Editorials

A reduced risk of Alzheimer’s disease in those who survive cancer

BMJ 2012; 344 doi: http://dx.doi.org/10.1136/bmj.e1662 (Published 12 March 2012) Cite this as: BMJ 2012;344:e1662
  1. Mary Ganguli, professor of psychiatry, neurology, and epidemiology
  1. 1University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
  1. gangulim{at}upmc.edu

Cold comfort for individual patients?

In a linked population based cohort study (doi:10.1136/bmj.e1442), Driver and colleagues report that older adults who survived cancer had a lower risk of developing Alzheimer’s disease than those who had never had cancer. Furthermore, people with Alzheimer’s disease had a lower risk of subsequent cancer than those without the disease.1 This report of an apparent mutually protective relation between Alzheimer’s disease and cancer is intriguing although not unprecedented. Others have previously hinted at such a link,2 3 4 and a similar pattern has been described for cancer and Parkinson’s disease.5 So, are neurodegeneration and cancer inversely associated? Should doctors tell their patients with newly diagnosed cancer that they have a reduced risk of Alzheimer’s disease (or vice versa)?

Epidemiologists dream of discovering new risk (or protective) factors for disease. However, the path of analytical epidemiology is littered with observational findings that briefly made headlines but then failed to be replicated by other observational studies, or to be borne out by experimental studies. We should search diligently for alternative explanations for new observed associations because the inevitable backlash against results that are not confirmed by other studies tends to deepen scepticism about epidemiological research.6

Hazard ratios compare the hazard of disease in people who are …

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