Sorting through the Confusion: Is there a Link between Breast Cancer and Alzheimer’s Disease?

In the worldwide quest for what causes Alzheimer’s, there has been some data and much speculation around whether there is a definitive connection between breast cancer treatments, such as chemotherapy, and this degenerative brain disorder. A recent study basically concluded, “Well, it depends.”

There’s no denying that breast cancer treatment can cause at least temporary cognitive issues (anywhere from weeks to years). Colloquially known as “chemo brain,” the American Cancer Society lists a few common symptoms of this condition such as:

• A patient forgetting things that they usually have no trouble recalling (memory lapses)
  
• Trouble concentrating (a patient can’t focus on what they’re doing, have a short attention span, or may “space out”)
  
• Trouble remembering details like names, dates, and sometimes larger events
  
• Trouble multitasking
  
• Taking longer to finish things (a patient becoming more disorganized, with slower thinking and processing)
  
• Trouble remembering common words (a patient unable to find the right words to finish a sentence)

If any of this sounds familiar, that’s because it is. Some of these symptoms are what is often experienced by a patient suffering from Alzheimer’s disease. But similarity does not necessarily equal a real connection between the two. And research needs to determine where breast cancer fits in the puzzle to uncover what causes Alzheimer’s.

Unfortunately, the results of research to date are mixed. One study showed an increased risk of cognitive conditions in woman that received chemotherapy. Another study of twins correlated cancer survivors and an increased risk of cognitive impairment compared to a twin with no history of cancer. But another study negates the link between dementia and breast cancer treatment, while another actually showed a reduced risk of Alzheimer’s disease connected to patients with a history of cancer.

Age, Cancer and Alzheimer’s Disease

The vast majority of Alzheimer’s cases strike a patient late in life. And advancing age also increases a person’s risk of developing breast cancer. But most cancers typically appear outside of a patient’s central nervous system, so what is the link? What current research is demonstrating is that while the link may or may not be direct, there is an increase in risk for older patients that have received chemotherapy treatment.

Chemotherapy can extend a person’s lifespan, but that advancing age can also increase the risk for Alzheimer’s disease. And since the cognitive impairment side effects of cancer treatment can last for years, this can bring together a merging of risk factors. Chemotherapy may affect how the brain “ages” and it could create the condition for a brain profile like what is seen in patients with Alzheimer’s disease. This recent study shows that survivors with a history of chemotherapy treatment had a significantly higher probability of developing Alzheimer’s compared to those who were not treated for cancer. But the authors of the study admit that these results do not show that either cancer or its treatments cause Alzheimer’s disease directly. It simply shows that cancer and chemotherapy can negatively impact the same regions of the brain that are also affected by Alzheimer’s. It also shows that a person’s age can impact their overall level of risk.

Genetics and Alzheimer’s Disease

Another find in the study was that patients with a genotype known as APOE ɛ4 that were treated chemotherapy had an increased risk of developing Alzheimer’s disease compared to those that did not receive chemotherapy. This genotype is associated with the proteins that can build up to cause Alzheimer’s. And chemotherapy may impair the body’s natural mechanisms to clear out these toxins. This shows the impact genetic testing can have in evaluating Alzheimer’s risk in the future.

Many Questions Still Need Answers

The research to date still leaves many questions unanswered. Larger sample sizes and additional studies are needed to verify results. The authors of the study encourage this, as well as further work with machine-learning algorithms in combination with neuroimaging data to evaluate risk of progressive chemotherapy-related brain injury.

Research also needs to consider the impact of factors such as radiation treatments, the type of cancer present, duration and doses of chemotherapy and pre-existing cognitive conditions to really understand the exact nature of the relationship between breast cancer, its treatments and the impact on the potential for Alzheimer’s disease.

But every new piece of data is a step forward, and each new study can provide another brick in the road to finally understanding what causes Alzheimer’s.