It may seem a small consolation from either point of view, but a new study has affirmed that patients with cancer are less likely to develop Alzheimer's disease, and patients with Alzheimer's disease are less likely to get cancer.
"There were still people who had both Alzheimer's and cancer, but it was significantly less common than we would expect," says lead author Catherine M. Roe, Ph.D., research instructor in neurology at Washington University School of Medicine in St. Louis. "If there truly is an inverse association, it gives us one more way of finding out what's going wrong in both cancer and Alzheimer's, and that could lead us to new ways to treat either condition."
The study appears online Dec. 23 in the journal Neurology.
Hints of a disconnect between cancers and neurological disorders have been building for years. The effect was first noticed in patients with Parkinson's disease, who get cancer less often; later studies have suggested that multiple sclerosis sufferers may have fewer tumors, and that Down syndrome patients who live to middle age or older have reduced incidence of cancer.
Six years ago, Maria Behrens, M.D., then a postdoctoral fellow at Washington University's Alzheimer's Disease Research Center (ADRC), noticed that few nursing home patients in her native Chile seemed to have cancer. Roe, Behrens and their colleagues conducted a study using data from research volunteers at the ADRC and found that people with Alzheimer's disease were slower to develop cancer in the future.
For the new study, scientists followed 3,020 people aged 65 and older enrolled in the Cardiovascular Health Study, a National Heart, Lung, and Blood Institute Study that gathered extensive health data on its participants. ADRC researchers monitored the subjects for an average of five years to see if they developed dementia and for an average of eight years to see if they were hospitalized for cancer. As the study began, 164 patients already had Alzheimer's, and 522 patients had been diagnosed with cancer.
During the study, 478 people developed dementia, and 376 developed invasive cancer. Those who had Alzheimer's disease at the start of the study were 69 percent less likely to be hospitalized for cancer treatment than those who did not have Alzheimer's when the study began. Caucasian people who had cancer as the study began had 43 percent less risk of developing Alzheimer's disease. The latter finding, however, was not apparent in minority groups.
To make sure that doctors or caregivers treating Alzheimer's patients weren't just too overwhelmed to notice the start of cancer, researchers also monitored cancer incidence in patients with vascular dementia. Scientists think this condition is caused by lack of blood to the brain.
"If the decreased chance of cancer diagnosis was simply due to the fact that physicians don't notice cancer in people with dementia, the decrease should have shown up for both the Alzheimer's patients and those with vascular dementia," Roe says. "But the drop in cancer risk was only seen in those with Alzheimer's."
Could Alzheimer's be killing patients before they can be diagnosed with cancer? Roe says epidemiologists have analytical techniques to adjust for such deaths. She also notes that patients with vascular dementia tended to die sooner than patients with Alzheimer's, yet they still had a higher risk of cancer than patients with Alzheimer's.
Roe cautions that the study was based on cancer hospitalization data, meaning that cases of benign, inoperable or otherwise untreated cancers could not be considered. She and her colleagues plan to study a larger patient population to see if Alzheimer's disease changes risks of specific types of tumors, and if certain types of cancers have larger or smaller effects on Alzheimer's risk.
Roe CM, Fitzpatrick AL, Xiong C, Sieh W, Kuller L, Miller JP, Williams MM, Kopan R, Behrens MI, Morris JC. Cancer linked to Alzheimer's disease but not vascular dementia. Neurology, Dec. 23, 2009.
Funding from the National Institutes of Health, the National Heart, Lung, and Blood Institute, the National Institute of Neurological Disorders and Stroke, the National Institute on Aging, the Washington University Alzheimer's Disease Research Center and the National Center for Research Resources supported this research.
Washington University School of Medicine's 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children's hospitals. The School of Medicine is one of the leading medical research, teaching and patient care institutions in the nation, currently ranked third in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children's hospitals, the School of Medicine is linked to BJC HealthCare.