BOSTON—Patients with various types of cancer have a decreased risk for Alzheimer’s disease, according to research presented at the 2013 Alzheimer’s Association International Conference. Among patients treated for cancer, chemotherapy treatment further decreased the risk of Alzheimer’s disease.
A majority of cancers, including pancreatic, lung, and liver, were associated with a 10% to 51% decreased risk of Alzheimer’s disease, reported Jane A. Driver, MD. Exceptions to the pattern were screening-related cancers such as prostate cancer and melanoma, which were positively associated with a risk for Alzheimer’s disease. “The most frequent pattern is that patients who survived cancers had a lower risk of Alzheimer’s disease, lower than the rest of the population and people without cancer,” said Dr. Driver, of the Boston VA Medical Center, Associate Physician at Brigham and Women’s Hospital, and Assistant Professor of Medicine at the Harvard Medical School. “We have an inverse association.”
The findings are the latest evidence from a decade’s worth of research by Dr. Driver and others who have explored whether a true inverse relationship existed between cancer and Alzheimer’s disease. In the July 23 issue of Neurology, Musicco et al found that older persons with cancer have a reduced risk of Alzheimer’s disease dementia and vice versa.
Analysis of a National Veterans Cohort
Dr. Driver, along with coauthor Laura Frain, MD, and their colleagues, investigated the relationship between 19 types of cancer, Alzheimer’s disease, and chemotherapy using data from the National Veterans Health System Cohort, a large clinical database of about 5 million persons. All 3.5 million eligible participants were 65 and older, had received outpatient care between 1997 and 2001, and did not have dementia at baseline. After an average of 5.7 years of follow-up, 771,285 people had developed cancer and about 82,000 had developed Alzheimer’s disease.
Analysis revealed that liver cancer was associated with a 51% lower risk of Alzheimer’s disease compared with no history of cancer; pancreatic cancer was associated with a 44% lower risk; esophageal cancer had a 33% decreased risk; leukemia had a 31% lower risk; and lung cancer had a 25% decreased risk. Head and neck cancer, lymphoma, myeloma, and kidney cancer also had an inverse relationship with Alzheimer’s disease.
Two types of cancer, however, had a positive association with Alzheimer’s disease. Melanoma was associated with a 14% increased risk of Alzheimer’s disease, and prostate cancer with an 11% increased risk. Other types of cancer, including colorectal, stomach, bladder, genital, thyroid, sarcoma, and brain, had no significant association with Alzheimer’s disease.
All cancers combined were assoicated with a 3% increased risk of Alzheimer’s disease, but this finding was mostly driven by prostate cancer, which is by far the most common cancer in the veteran cohort, noted Dr. Driver. “Why would we see that only screening-related cancers have a positive association with Alzheimer’s disease?” she asked. “It could be a number of things. One is that these are people under increased surveillance. Many of them are getting diagnosed with cancer because we are looking for it. Many of them have very early-stage cancer. That’s totally different than lung cancer, where people will present with a cancer, usually at a more advanced stage without someone screening. It’s possible that people diagnosed with screening-related cancers, like melanoma, colorectal, and prostate, would also be at increased risk of being diagnosed with other things…. There’s a bias there, especially in our population that is heavily screened, where we’re seeing this different pattern in cancers for which we do screen.”
Dr. Driver’s group also examined the relationship between Alzheimer’s disease and other age-related diseases such as stroke, osteoarthritis, cataracts, and macular degeneration. “We found that in each case, people who had cancer were at increased risk of those diseases, in stark contrast with the pattern we saw with Alzheimer’s disease,” said Dr. Driver.
A Protective Effect of Chemotherapy?
A further intriguing finding, according to Dr. Driver, was that cancer patients who had received chemotherapy or radiation had an additional decreased risk of Alzheimer’s disease of 17% to 23%.
“The decreased risk of Alzheimer’s disease in this population is not fully explained by chemotherapy use or treatment,” she commented. “It’s there regardless of that. But then it seems in those who are treated for cancer, chemotherapy further decreases the risk. And we figured that out by doing another study in which we’ve just looked at people with cancer and compared those who got chemotherapy and those who didn’t and saw that there was a 20% to 45% decreased risk of Alzheimer’s disease in cancer patients who received chemotherapy.”