Although the occurrences of both cancer and Alzheimer disease (AD) increase exponentially with age, an inverse relationship between the two illnesses has been found. Older persons with cancer have a reduced risk for developing AD, and older persons with AD have a reduced risk for developing cancer.
“AD dementia, cancer, and senescence could be manifestations of a unique phenomenon related to human aging,” wrote Massimo Musicco, MD, of the National Research Council of Italy, in Milan, and fellow investigators in Neurology.
Musicco and colleagues used various health registries to derive cancer incidence as well as AD incidence. They then calculated the expected cases of AD dementia in persons with a new diagnosis of cancer and the expected cases of cancer in persons with AD.
During the six-year period covered, among 204,468 residents of Northern Italy aged 60 years and older, 21,451 developed cancer and 2,832 developed AD. Although 281 of persons with cancer were expected to have AD and 246 with AD were expected to have cancer, only 161 subjects had both diseases. Persons with AD had a 50% reduced risk for cancer, and people with cancer had a 35% reduced risk for AD. These results were maintained in almost all subgroup analyses.
Musicco noted that the reduced risks for cancer and AD in patients who already had one of these diseases has been seen in other studies, but that his team’s was the largest such study to date. Musicco also pointed out that his research has several strengths over previous studies, such as looking for the presence of the second disease both before and after the diagnosis of the first disease.