The association was first noticed in 2005 when researchers looked at how many people over 65 with cancer later developed Alzheimer’s, and vice versa. To further explore the link, Massimo Musicco at the Institute of Biomedical Technology in Milan, Italy, and his colleagues recorded cancer and Alzheimer’s diagnoses for over a million people by looking at registries of drug prescriptions and hospital admissions between 2004 and 2009. In each case of cancer or Alzheimer’s, they checked for the other disease before the person was treated, as well as in the years after.
Previous studies have examined the possible relationship between Alzheimer’s and cancer in old age, but Musicco said the studies did not utilize enough research subjects.
“All the papers reported a negative association between the two diseases, but the number of people being studied was quite small,” he said.
Looking to use a larger group of people for observation, Musicco analyzed a population of 204,468 people in northern Italy aged 60 and over during a six-year period. Over the course of that time, 21,451 people developed cancer and 2,832 people developed Alzheimer’s disease.
The results showed that a total of 161 people had both cancer and Alzheimer’s disease.
Based on how frequently these diseases develop in the general population, that number would have been expected to be 281 for cancer and 146 for Alzheimer’s disease. Instead, the risk of cancer was significantly reduced by half for people with Alzheimer’s disease, while the risk of Alzheimer’s disease for people with cancer decreased by 35 percent.
“It’s a very convincing demonstration of the links between two pathologies that we often think of as separate,” says Richard Faragher of the British Society for Research on Ageing. “The question is: what is going on?”
Although both diseases are linked to ageing, they work in very different ways. While cancer results from the uncontrolled growth of cells, Alzheimer’s is related to the death of brain cells.
“There may be some genetic factor that, if it’s tipped one way, it may cause abnormal cell growth, and tipped another way, it may cause abnormal cell death,” says Catherine Roe at Washington University in St Louis, who first reported the association. She suggests a tumour-suppressing gene called TP53 might play such a role. Its activity is elevated in people with Alzheimer’s disease, but inactivated in about 50 per cent of cancer tumours, she says.
The link between the two may also be explained by the ageing of cells. As we get older, many of the body’s cells undergo senescence – a process that stops them dividing and triggers the release of inflammatory proteins. This is thought to protect us from cancer, the idea being that any ageing cells that have accumulated DNA damage are destroyed, perhaps by the immune response triggered by the proteins.
But senescence may also be linked to neurodegenerative diseases. Last year, Claudio Torres at Drexel University College of Medicine in Philadelphia found huge numbers of cells that had stopped dividing in the brains of people who had died of Alzheimer’s.
People may have cells that are more or less likely to senesce, protecting them from one disease, but putting them at risk of the other, says Faragher. We need to look for ways to selectively kill senescent cells or ameliorate their effect, he adds. “This opens entirely new routes for treatment for quite a lot of conditions.”
Sources: New Scientist, Fox News
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