The Growing Link Between Cancer and Alzheimer’s Disease

People with cancer had a slower rate of memory decline both before and after diagnosis, compared with people who were cancer-free, according to the results of a population-based cohort study recently reported in JAMA Network Open. Previous research has shown an inverse association between developing cancer and Alzheimer’s disease, and this study provides further support for this relationship.

The study cohort was made up of 14,583 adults from the Health and Retirement Study who were born before 1949 and had no diagnosis of cancer by 1998. Participants were followed from 1998 to 2014, and during those 16 years, a total of 12,333 participants remained cancer-free and 2,250 developed cancer.

A survey was conducted in 1998 to set a baseline; during the follow-up period, telephone or in-person biennial interviews were conducted to gather additional information, such as whether a participant had been diagnosed with cancer. Proxy interviews were permitted for adults who were too impaired to answer by themselves.

Memory function was assessed throughout follow-up. To assess memory function, participants were asked to recall a 10-word list both immediately and after a delayed period of time. For participants who were too impaired, a proxy was asked to evaluate the individual’s memory according to a 5-item Likert scale and complete the 16-item Informant Questionnaire for Cognitive Decline.

“This is a very important contribution to the literature,” Jane Driver, MD, Division of Aging, Brigham and Women’s Hospital, told Cancer Network.  “[The study] provides a level of evidence that’s stronger than a lot of prior studies, which were really only able to look at overall associations using diagnoses. Here, we actually have a diagnostic test that’s actually measuring cognition and its change over time.”

The study revealed that before a cancer diagnosis was made, participants had a 10.5% (95% CI, 6.2%–14.9%) slower rate of memory decline compared with participants who remained cancer free. After a new cancer diagnosis, the memory appeared to decline but this effect was transient. After a cancer diagnosis, cancer survivors had a 3.9% (95% CI, 0.9%–6.9%) slower rate of memory decline compared with cancer-free individuals. 

Driver said this is a population-based study and the authors were able to look at large numbers of patients, which is “really necessary” to try to answer the question of whether cancer and Alzheimer’s disease were inversely related. In addition, she applauded the study authors’ use of cognitive assessments over time.

“Both before and after the cancer diagnosis, overall, people who develop cancer seem to develop cognitive impairment more slowly than the comparison subjects,” said Driver. “That does really suggest that there’s something to this inverse association, and that maybe it’s not all due to some kind of a bias, which many people have attributed this relationship to over the years.”
About the inclusion of proxy assessments, Driver was not particularly critical, explaining that it’s “to be expected” that as people age and their cognition gets worse, they’re going to need a proxy to provide the information.

“The take home [message] is that it’s worth pursuing the underlying biological explanations for this because although there’s many treatments for cancer, we don’t yet have one effective treatment for Alzheimer’s disease,” said Driver. “I think that many of us are hoping that further investigation of this strange association would perhaps lead us closer to a treatment for Alzheimer’s or at least understanding it better than we have so far.”