An interesting article was published in the British Medical Journal (April, 2012). Based on recent data from the Framingham Heart Study, survivors of malignant cancers have a lower risk of developing Alzheimer’s disease and those with Alzheimer’s disease have a lower risk of cancer.

The Framingham Heart Study is a longitudinal study began in 1948 with over 5,000 participants ranging in age from 28-62. A second phase of the study enrolled children of the original participants beginning in 1971. A subset of these groups (who were not demented) was followed for 10 years to provide the data for this study.

The cancer survivors had 33% less risk of developing Alzheimer’s disease than comparison subjects who never had cancer. Interestingly, survivors of smoking related cancers were less likely to develop Alzheimer’s disease than survivors of nonsmoking related cancers – however, they had a substantially higher risk for having a stroke.

Furthermore, having Alzheimer’s disease reduced the risk of being diagnosed with cancer. Of course, this side of the equation may be a result of under reporting cancer symptoms in those already diagnosed with Alzheimer’s disease. However, two studies demonstrated decreased incidence of cancer upon autopsy of deceased Alzheimer’s patients. Further, Japanese survivors of the atomic bombs who were diagnosed with Alzheimer’s disease had a substantially lower incidence of cancer but those diagnosed with vascular dementia had a greater incidence of cancer.

Two other prospective studies have produced the same pattern of reduced risk in cancer survivors when studying the association of cancer with Alzheimer’s disease. The same pattern of findings is also found for those diagnosed with Parkinson’s disease indicating that the correlation is not unique to Alzheimer’s disease.

Explanations of these intriguing findings are scarce. There may be some biological mechanism that links neurodegenerative diseases with cancer. Maybe some treatments, chemotherapy and radiation, for cancer may have a protective effect against neurodegeneration – despite their negative impact on cognition. These are very interesting data in need of explanation in future research as long as we don’t get so bogged down with preserving the amyloid hypothesis that we ignore other potentially useful directions.