Why People Who Have Survived Cancer Are Less Likely to Develop Alzheimer’s Disease

A new study in mice, published in the journal Cell, may shed light on the surprising link between cancer and Alzheimer’s disease.

Doctors have long observed that people who have survived cancer are less likely to suffer from Alzheimer’s disease, while tumors are less common among patients with dementia. Until now, there has been no clear biological explanation for this phenomenon.

Using a mouse model, scientists discovered a possible mechanism that could explain this connection. Alzheimer’s disease is associated with the accumulation of toxic protein plaques of beta-amyloid in the brain. These plaques disrupt communication between neurons, trigger inflammation, and gradually lead to memory loss and cognitive decline.

When mice were implanted with human tumors from the lungs, prostate, or colon, their brains stopped accumulating the typical amyloid plaques. In some experiments, the rodents’ memory even improved compared to a control group without tumors.

The researchers found that a protein called cystatin C, produced by tumors and released into the bloodstream, may be responsible. In the brain, this protein can bind to small clusters of beta-amyloid and “mark” them for destruction by microglia — the brain’s immune cells that act as a cleanup system. In mice with tumors, cystatin C activated the Trem2 receptor on microglia, shifting them into a more active state capable of clearing plaques more effectively.

However, it is important to note that these findings are based on experiments in mice, not humans. Mouse models reflect only part of the complex processes involved in Alzheimer’s disease, and it is still unknown whether tumors in real patients produce enough cystatin C or deliver it to the brain as effectively. Nevertheless, these results open new directions for future research and may help in developing treatment strategies aimed at activating the brain’s natural mechanisms for clearing pathological proteins.

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