Cancer patients are less likely to develop dementia (Alzheimer's disease), and dementia patients are less likely to have cancer. This has been proven through various large-scale studies, but there have also been criticisms that the statistics may be a result of a statistical illusion or survival bias, as cancer patients may not live long enough to develop dementia.
Research results suggest that cancer patients are less likely to develop dementia because certain cancer cells send protective signals to the brain through the bloodstream, helping to eliminate toxic proteins that cause dementia. A research team from Anglia Ruskin University in the UK reported this finding while investigating the relationship between cancer and dementia in mice.
The research team observed what changes occurred after transplanting tumor cells from human lung cancer, prostate cancer, and colon cancer under the skin of mice with dementia. According to the study, mice that received cancer cell transplants showed a halt in the accumulation of amyloid beta in the brain, unlike normal mice, and in some experiments, there was even an improvement in the memory of these mice, which had previously dropped significantly.
The research team identified a specific protein (cystatin-C) secreted by tumors as the key cause of this phenomenon. Cystatin-C, secreted by cancer cells, passed through the blood-brain barrier, which protects the brain, and penetrated into the brain. It then attached itself to amyloid beta aggregates, leaving a marker (tag) for immune cells (microglia) that act as cleaners in the brain to find it more easily. It was confirmed that it particularly activated the Trem2 sensor in microglia, stimulating them to strongly destroy toxic substances.
This research result (Peripheral cancer attenuates amyloid pathology in Alzheimer's disease via cystatin-c activation of TREM2) was recently published in the international journal <Cell>.
This study is significant in proving that cancer and neurodegenerative diseases are closely linked. It particularly shows an interesting paradox where substances secreted by cells causing disease in one organ can serve as cleaning tools to prevent dementia in another organ.
Cancer and dementia are diseases that people fear greatly, but it is very rare for both diseases to occur simultaneously in one person. The medical community has noted the statistical fact that cancer survivors have a lower risk of developing dementia, and dementia patients also have a lower risk of developing cancer.
According to the largest study ever conducted (July 2024) by a research team at Imperial College London, which tracked 3 million Britons over the age of 60 for about 9 years, cancer survivors were found to be 25% less likely to develop dementia than those without a history of cancer. A recent comprehensive analysis of major studies over the past decade by a Chinese pharmacy school found that dementia patients are 47% less likely to develop cancer, and cancer patients are 39% less likely to develop dementia.
However, the reason for this phenomenon has not been known. Although it is an animal experiment, a clue to solving this mystery has been discovered this time. The research team expects that it will be possible to develop new treatments that mimic the action of cystatin-C rather than utilizing the disease of cancer itself.
[Frequently Asked Questions]
Q1. Does this mean that the fact that cancer patients are less likely to develop dementia is not a statistical illusion?
A1. The medical community has raised the possibility that the short life expectancy of cancer patients may lead to a 'survival bias' where they do not survive long enough to develop dementia. However, this study has proven through mouse experiments that a specific substance (cystatin-C) secreted from cancer cells travels through the blood to the brain and directly removes dementia-causing substances, indicating a biological mechanism. This increases the likelihood that it is a protective action occurring in the body, beyond a simple statistical phenomenon.
Q2. What role does the 'cystatin-C' secreted by cancer cells play?
A2. Cystatin-C passes through the blood-brain barrier, which is the brain's protective barrier, and then attaches to amyloid beta protein aggregates, which are the main culprits of dementia. It acts as a kind of 'tag'. When this marking is left, the immune cells in the brain, microglia, can find the toxic substances more easily, and it activates a sensor called Trem2 (TREM2) to stimulate them to engulf it.
Q3. Does the conflict between cancer and dementia apply to all cancers?
A3. This study confirmed the effects with tumor cells such as lung cancer, prostate cancer, and colon cancer. Additionally, a large-scale follow-up study at Imperial College London in the UK also observed a common phenomenon of reduced dementia risk across major cancer types, including breast cancer. This suggests that it is not limited to specific cancers, but that the universal characteristics of cancer cells may influence neurodegenerative diseases.
