Alzheimer's linked to less cancer, and vice-versa
Seniors with Alzheimer's disease have a lower risk of cancer than other elderly adults – and seniors with cancer have a lower risk of Alzheimer’s, according to a new study published yesterday in the journal Neurology.
The inverse link between Alzheimer’s and cancer could be due to a number of genes that affect both neurology and cancer growth, and pathways by which the two are connected, explained the researchers conducting the study at the National Research Council of Italy's Institute of Biomedical Technologies.
"Cancer and Alzheimer's have been viewed by researchers as completely separate," said study leader Dr. Massimo Musicco. "Some of the knowledge that we have on cancer can be used for a better understanding of what happens when a person has Alzheimer's disease, and vice versa."
Similarly, recent evidence also suggests that Parkinson's disease is linked to a lower risk of cancer, according to Dr. Jane Driver, an aging expert at Brigham and Women's Hospital. She points out that the same pattern has been showing up for other neurological disorders too, including schizophrenia and Alzheimer's.
Earlier studies, however, have been inconclusive as to whether Alzheimer's disease may be preventing cancer symptoms from being noticed, and vice-versa, or whether those who die from either disease simply didn’t have a chance to be diagnosed with the other.
In the study conducted by Musicco, he and his research team found that those who ended up being diagnosed with Alzheimer's had a lower risk of cancer, not just leading up to their diagnosis, but after it as well.
Likewise, those who developed cancer were less likely to get Alzheimer's, both before and after the cancer was diagnosed.
"I'm hoping this will then convince all the doubters that there is a true inverse association between Alzheimer's, Parkinson's and probably some other neurologic diseases and cancer," Dr. Driver told Reuters Health.
For the study, Musicco and his colleagues followed 204,000 people in Northern Italy aged 60 and older for new cases of cancer and Alzheimer's disease.
Just over 21,000 of them were diagnosed with cancer between 2004 and 2009, with close to 3,000 diagnosed with Alzheimer's disease. There were 161 people diagnosed with both diseases.
Based on age and gender, the researchers calculated that 246 cases of Alzheimer's disease would be expected among those with cancer, and 281 cancers would be expected among those with Alzheimer's.
In other words, the researchers predicted that those with cancer were 35 percent less likely to develop Alzheimer's disease than other adults, and those with Alzheimer's were 43 percent less likely to develop cancer. And the association between the two held up when they looked at most cancers individually.
"These two diseases seem intrinsically related to human aging," Musicco told Reuters Health.
"Cancer may be conceptualized as a high tendency of cells to reproduce, which is so high that it is no (longer) controlled,” he said. “Alzheimer's disease is exactly the reverse. It's a sort of incapacity of neuron cells to reproduce."
According to Dr. Driver, what the study did not prove is that one disease is protective against the other, or that those with Alzheimer's never have to worry about getting cancer, and vice-versa.
As the research team admitted, there were some factors they couldn’t take into account, such as people’s lifestyle and other habits that could influence their risk of getting cancer and/or Alzheimer’s.
What the study about the inverse link has done, says Driver, is prompt more “thinking outside the box" as it pertains to treating Alzheimer's, a disease that has few good treatment options available at this time.
"By further investigating this decreased risk, there's a good chance we'll be able to find completely new therapies," Driver said. "Any new lead or any new avenue to go down, we really need to take it."
SOURCE: Neurology, "Inverse occurrence of cancer and Alzheimer disease", Massimo Musicco, MD, et al (published online July 10, 2013) doi: 10.1212/WNL.0b013e31829c5ec1