Fewer Alzheimer’s Diagnoses Seen in Cancer Patients Likely Result of Shorter Life Spans, Study Says

Studies suggesting that a cancer diagnosis reduces the risk of Alzheimer’s disease (AD), possibly through a biological mechanism that triggers cancer and prevents AD, may be somewhat irrelevant, researchers said, pointing to data showing that pancreatic cancer patients usually don’t live long enough to develop Alzheimer’s. The study, “Is Cancer Protective for Subsequent Alzheimer’s Disease Risk? Evidence from The Utah Population Database,” was published in The Journals of Gerontology Series b.

“Diagnosis of age-related diseases, such as Alzheimer’s disease, depends on someone surviving to an age when disease onset can occur,” Heidi Hanson, PhD, MS, the study’s lead author, a Huntsman Cancer Institute research associate and research assistant professor of family and preventive medicine at the University of Utah School of Medicine, said in a press release.

The research team led by Dr. Hanson compared pancreatic cancer patients with the cancer-free population to find that as the cancer-free population aged from 75 to 89, the rate of Alzheimer’s diagnosis increased from 2.5 to 7.5 percent, but it remained constant in pancreatic cancer patients, with only 2 percent being diagnosed with AD. Pancreatic cancer deaths are the highest among people between 75 and 84 years of age, with a median age at death of 73 years. This is the same age at which AD is usually diagnosed.

Ken Smith, PhD, one of the study’s senior authors, compared pancreatic cancer with gunshots in regard to protection against Alzheimer’s disease: “People who are shot rarely get Alzheimer’s because most of them die before they have the chance to. But no one would say that gunshot wounds protect against the disease.”

Researchers examined data from 92,245 people in the Utah Population Database, who were between 65 and 79 years old in 1992 and without any record of dementia. The study included both patients with and without pancreatic cancer, who were followed for at least 18 years to determine those later diagnosed with AD.

The investigators used three different statistical methods to show that cancer patients not only had higher mortality rates but that, contrary to previous studies, they also did not have a lower risk of developing Alzheimer’s disease.

To further test their idea, two groups of patients with early stage or metastasized prostate cancer were analyzed. Researchers hypothesized that if cancer provided protection against AD, patients with the same cancer type would be similarly protected, and their likelihood of developing Alzheimer’s would be the same. However, they found that patients with metastasized prostate cancer had decreased risk for AD, which correlated with a reduced life expectancy. Consistently, when the results were adjusted for mortality, this difference was no longer statistically significant.

“These results call into question a protective association between cancer and Alzheimer’s. If we are going to understand aging-related diseases, we need to consider how other chronic diseases and conditions impact them,” Dr. Hanson concluded.