Cancer Linked to Decreased Risk of Alzheimer's

A pair of recent studies finds that those with a history of cancer have up to a 51% reduced risk of developing Alzheimer’s disease.

The results of 2 new studies add to the growing body of evidence suggesting that having had cancer lowers one’s risk of developing Alzheimer’s disease.

The first study, published online on July 10, 2013, in Neurology, suggests a reciprocal relationship between cancer and Alzheimer’s, in which having either protects against developing the other. Researchers in Northern Italy conducted a cohort study including more than a million residents. Data on cancer incidence was collected from the local health authority tumor registry and information on Alzheimer’s incidence was taken from prescription drug registries, hospitalizations, and payment exemptions for special disease conditions.

The researchers calculated the expected number of Alzheimer’s cases in patients with newly diagnosed cancer by applying Alzheimer’s incidence rates specific to age, sex, and calendar year that were observed in the entire population from 2004 to 2009. The same procedure was used to calculate the number of expected cancer cases in Alzheimer’s patients. Separate analyses were conducted for different types of cancer and for the period before and after diagnosis for survivors and non-survivors.

The results indicated that Alzheimer’s patients had a 50% reduced chance of developing cancer, and cancer patients had a 35% reduced chance of developing Alzheimer’s. The relationship observed between the 2 conditions was seen in almost all subgroup analyses.

The second study, presented on July 15, 2013, at the Alzheimer’s Association International Conference in Boston, also evaluated the risk for Alzheimer’s disease in cancer patients, looking at the association in 19 specific types of cancer as well as in cancer treatment.

The researchers analyzed the health records of nearly 3.5 million military veterans aged 65 and older who received treatment through the Department of Veterans Affairs from 1996 to 2011 and who had no form of dementia at the beginning of the study. During a median follow-up period of 5.65 years, 82,028 participants were diagnosed with Alzheimer’s disease.

Analysis of the study’s findings indicated that most types of cancer included were associated with a decreased risk of Alzheimer’s. The greatest risk reduction was found in those who had had liver cancer (51% reduction in risk), followed by pancreatic cancer (44%), esophageal cancer (33%), myeloma (26%), lung cancer (25%), and leukemia (23%). Cancers that were not associated with a decreased risk of Alzheimer’s or that were associated with an increased risk included melanoma and prostate and colorectal cancers.

The researchers found that having undergone chemotherapy further reduced patients’ risk of developing Alzheimer’s. Among participants with a cancer history, those who had been treated with chemotherapy but not radiation had a 20% to 45% decrease in risk for Alzheimer’s, depending on cancer type. Patients who had received chemotherapy for prostate cancer, however, had no reduction in Alzheimer’s risk.

“Together, these findings indicate that the protective relationship between most cancers and Alzheimer's disease is not simply explained by increased mortality among cancer patients,” said lead study author Laura Frain, MD, a geriatrician at VA Boston Healthcare System, in a press release. “More research is needed to determine if these results have therapeutic implications for Alzheimer’s.”