Most kinds of cancer are associated with a significantly decreased risk of Alzheimers disease, according to a study of 3.5 million veterans reported Monday at the Alzheimers Association International Conference in Boston.
In addition, the study suggested that chemotherapy treatment for almost all of those cancers conferred an additional decrease in Alzheimers risk.
A growing body of evidence suggests a possible association of cancer with reduced risk for Alzheimers disease, but whether the association differs between cancer types or is modified by cancer treatment has not been clarified, according to the researchers.
Laura Frain, MD, a geriatrician at VA Boston Healthcare System, and colleagues analyzed the health records of 3,499,378 veterans ages 65 and older who were seen in the VA healthcare system between 1996 and 2011 and who were free of dementia at baseline. The objective was to evaluate the relationship between a history of 19 different cancers, cancer treatment and subsequent Alzheimers disease.
Over a median follow-up of 5.65 years, 82,028 veterans were diagnosed with Alzheimers. Of those veterans with Alzheimers, 24% had a history of cancer.
The researchers found that most types of cancer were associated with reduced Alzheimers risk, ranging from 9% to 51%. Reduced risk was greatest among survivors of liver cancer (51% lower risk), cancer of the pancreas (44%), cancer of the esophagus (33%), myeloma (26%), lung cancer (25%) and leukemia (23%). Cancers that did not confer a reduced Alzheimers risk, or were associated with an increased risk, included melanoma and prostate and colorectal cancers.
The researchers found no association between cancer history and reduced risk of any other typical age-related health outcome. In fact, cancer was associated with an increased risk of stroke, osteoarthritis, cataracts and macular degeneration. Most cancer survivors also were at increased risk for non-Alzheimers dementia.
“Together, these findings indicate that the protective relationship between most cancers and Alzheimers disease is not simply explained by increased mortality among cancer patients,” Frain said in a news release. “More research is needed to determine if these results have therapeutic implications for Alzheimers.”
Among veterans with a cancer history, treatment with chemotherapy but not radiation reduced Alzheimers risk by 20% to 45%, depending on cancer type, with the exception of prostate cancer.
“The potential protective effect of chemotherapy is supported by recent experimental studies,” Frain said. “The results of this study are interesting because they could help focus future research onto the specific pathways and treatment agents involved in the individual cancers that are associated with a reduced risk of Alzheimers. This could potentially open new therapeutic strategies for Alzheimers prevention and treatment.”