Alzheimer's may guard against cancer and vice versa

Alzheimer's disease patient Isidora Tomaz (L), 82, is caressed by her husband Amilcar Dos Santos, also 82, in their house in Lisbon September 15, 2009.

NEW YORK (Reuters Health) - People with Alzheimer's disease may be less apt to get cancer and people with cancer may be less apt to get Alzheimer's disease, new research hints.

"Discovering the links between these two conditions may help us better understand both diseases and open up avenues for possible treatments," Dr. Catherine M. Roe of Washington University School of Medicine in St. Louis, noted in a written statement from the American Academy of Neurology.

According to a report published today in the academy's journal Neurology, Roe and her team studied 3,020 people aged 65 and older. These individuals were followed for an average of five years to see whether they developed dementia and an average of eight years to see whether they developed cancer.

At the start of the study, 164 people (5.4 percent) already had Alzheimer's disease and 522 people (17.3 percent) already had a cancer diagnosis. During the study, 478 people developed dementia and 376 people developed cancer.

The researchers found that, for people who had Alzheimer's disease at the outset, the risk of future cancer was reduced by 69 percent compared to those who did not have Alzheimer's disease when the study started.

For white people who had cancer when the study started, their risk of developing Alzheimer's disease was reduced by 43 percent compared to people who did not have cancer at the start of the study.

This effect, however, did not apply to minority populations. In fact, the opposite effect was observed in minority populations -- those who started out with cancer at the beginning of the study were more likely to develop Alzheimer's disease. However, the sample size of minorities starting off with cancer (29 individuals) was too small for the result to be considered significant.

Overall, the results of this study support previous findings that cancer and brain degenerative diseases such as Parkinson's and Alzheimer's disease may share common molecular underpinnings. However, Roe noted in an email to Reuters Health, "Since we found no associations between vascular dementia and cancer, we don't think that cancer is linked to dementia generally."

Vascular dementia, the second most common form of dementia after Alzheimer's disease, is caused by clogged blood vessels and other conditions affecting the blood supply to the brain. Based on the current study, only the degenerative form of dementia, and not the form caused by lack of blood to the brain, appears to be somehow protective against cancer.

In future studies, "We would like to examine whether relationships between cancer and Alzheimer's disease differ, depending on the type of cancer one has," Roe said.

SOURCE: Neurology, online December 23, 2009.