By Alan Mozes
Studying more than 200,000 older adults in northern Italy, the research team concluded that cancer patients bear a 35 percent lower risk for developing Alzheimer's, while people with Alzheimer's have nearly half the risk of getting cancer compared to the general population.
The investigators suggested that the findings could help guide researchers toward better treatments for both illnesses over the long term.
"Practically, our results [indicated that] some genes that have been demonstrated to act in cancer growth and control might also be involved in the [development] of Alzheimer's disease," said study lead author Dr. Massimo Musicco, of the National Research Council of Italy's Institute of Advanced Biomedical Technologies. "And this represents a promising [observation] for the struggle against this devastating neurodegenerative disorder."
For the study, which was published online July 10 in the journal Neurology, the research team spent six years (2004 to 2009) tracking the health status of more than 204,000 Italians aged 60 and older. During that period, nearly 21,500 men and women developed cancer, while more than 2,800 developed Alzheimer's disease.
Although 161 patients developed both diseases, the authors said that known incidence rates among the general population had predicted a higher dual-disease figure.
After crunching the numbers, the team found that having one disease seemed to have a considerable protective effect in terms of lowering the risk for the other.
The researchers also determined that the reduced-risk linkage could not be explained by fatalities from either disease. This meant that a lower risk for developing Alzheimer's could not simply be explained away by the premature death (and therefore shorter lifespan) of cancer patients, or vice versa.
Dr. James Galvin, a professor of neurology, psychiatry, nursing and nutrition at the NYU Langone School of Medicine in New York City, said that the observed linkage between cancer and Alzheimer's, while important, may not apply to less common forms of dementia.
"Interestingly, nearly all investigations have found that cancer and cancer treatment does not seem to alter the risk of developing other forms of dementia, such as vascular dementia caused by multiple strokes," he said.
"This suggests common pathways exist between most cancers and Alzheimer's disease, but these relationships do not appear to exist with other causes of dementia," Galvin said.
Given such a potentially unique connection between cancer and Alzheimer's, Galvin said, more research is now needed "to examine whether drugs used to treat cancers such as lung, leukemia, liver and pancreas may also be used to treat Alzheimer's."
In an editorial accompanying the Italian study, Catherine Roe, an instructor in neurology at the Washington University School of Medicine, in St. Louis, said the study's large size makes the findings exciting.
"Like previous studies, they have shown that people with Alzheimer's disease are less likely to get cancer, and people with cancer are less likely to get Alzheimer's disease," she said.
"But because they looked at so many people, they were also able to test whether Alzheimer's is associated with some kinds of cancers, but not other kinds," she said. "This may help in eventually pinpointing why there is this opposite relationship between Alzheimer's and cancer."
Although the study found a link between the risks of cancer and Alzheimer's, it did not prove a cause-and-effect relationship.