In The News: The Curious Link Between Alzheimer's Disease and Cancer

Introduction:

Why “In The News?”

As news coverage of Alzheimer’s Disease (AD) continues to grow, we want to help our readers examine scientific claims.

We will regularly comment on both consumer-focused media stories and more scientific ones, like today. Our readers will learn whether the physicians and scientists at the USC Epstein Family Alzheimer’s Therapeutic Research Institute (ATRI) recommend these therapies.

Our USC faculty are always exploring new potential therapies for care and cure. We conduct rigorous double blind, placebo-controlled trials of medications only after extensive preliminary research shows there is sufficient safety and efficacy data. These clinical trials are necessary to ascertain whether new treatments could be of genuine benefit to people with AD.

This week’s “In The News”: “The curious link between Alzheimer’s disease and cancer”

The claims explored in this article revolve around observations showing an inverse relationship between incidence of cancer and AD diagnoses.

Survival bias?

At first glance this seems easy. Alzheimer’s Disease is not only a devastating condition, it is common. Moreover, the greatest risk factor is age. The risk for developing Alzheimer’s disease steadily increases as we age. Though numbers vary, it is estimated that the risk doubles every 5 years after the age of 65.The number of women with AD is greater than the number of men because statistically women live longer.

Therefore,it is tempting to dismiss this inverse association by concluding that people with cancer die at a younger age and do not live long enough to develop AD.

Cannot simply conclude it is survival bias.

However, this inverse relationship appears reproducible, the studies show that cancer survivors have a lower rate of developing AD/dementia, and people with a diagnosis of AD reportedly have a substantially lower rate of receiving a cancer diagnosis than the age matched population. The Framingham Heart Study and the Three Million Meta-Analysis Study, published in 2012 and 2024 respectively, showed a 25-33 percent lower rate of AD/dementia diagnoses in cancer survivors.

Questions remain about how powerful the inverse relationship truly may be and whether the correlation is with AD or other related dementia diagnoses.

It could be argued that people with a dementia diagnosis may be less likely to pursue extensive testing for other health problems. As a result, cancers and other medical conditions might go undiagnosed in this group. It is also important to consider that the diagnoses of AD and dementia were made on a clinical basis, not PET imaging;one may conclude that all met the criteria for a diagnosis of dementia, but we cannot know how many had AD.

What could the relationship between cancer and AD be?

Mechanisms and a possible new treatment:

Cancer is characterized by relentless cell reproduction and AD by premature cell death. Could cancer cells produce agents which can renew dying cells? This is an intriguing possibility and finding reported by X Li. And colleagues in the journal Cell (2026) suggest that a protein called cystatin-c, which is produced by a number of tumors (including breast, colon, prostate, and renal cancer) can enter the brain and activate the cells which are responsible for clearing amyloid and other debris. These cells are called microglia. The scientists tested this hypothesis in a well-established mouse model of AD and found it to be highly beneficial.

Discussion:

Questions remain. The inverse relationship between cancer and AD is not proven and further study is needed now that it is possible to differentiate the causes of dementia using biomarkers. Epidemiological analyses need to assess other potential issues to determine whether patterns of medical care are different after a diagnosis of AD is made.

If the theory that indeed an inverse relationship exists between AD and cancer survival, other theories about the causes should also be explored, including chemotherapy exposures and their possible effects on the brain.

Conclusion:

The cystatin-C data is exciting, but it is mice, and we will need to test the safety and efficacy in humans before we can draw any conclusions. Still, at our Institute, we are always seeking new treatments and we believe we may need combinations of medications with different mechanisms to fight AD and related degenerative dementias. Perhaps a trial of cystatin-C could be seen in the future.