Decades of research have uncovered an unusual link between cancer and Alzheimer’s disease. For years, scientists have wondered why cancer and Alzheimer’s are rarely found in the same patients — raising the possibility that one disease may offer some protection against the other. Now, scientists in China say they have identified a potential explanation.

A new study suggests that a specific protein released by cancer cells may be able to cross the blood-brain barrier and interfere with the abnormal protein buildup associated with Alzheimer’s disease. Researchers found that this protein can break up amyloid plaques — a hallmark of Alzheimer’s — offering new insight into the complex relationship between cancer and neurodegenerative disorders.

The study, published in Cell, found that proteins from cancer cells were able to cross the blood-brain barrier in mouse models of Alzheimer’s disease. When researchers at Huazhong University of Science and Technology in Wuhan, China, injected these mice with three types of human cancer tumors — lung, prostate, and colon — the animals did not develop the characteristic plaques associated with Alzheimer’s.

The scientists then narrowed down the list of candidate proteins to one called cystatin C. In additional experiments, they found that cystatin C can bind to the molecules that form brain plaques. This process appears to send signals to a protein called TREM2 found on immune cells in the brain, which then prompts those immune cells to degrade the plaques. Study author Youming Lu, a neurologist, reported that the mice performed better on cognitive tests after the intervention.

Dr. Donald Weaver, a neurologist at the University of Toronto, said the findings provide an interesting “piece of the puzzle” in developing new therapies to treat Alzheimer’s disease. Identifying a protein that can activate TREM2 is especially valuable, he said, because scientists have been looking for ways to trigger that process for years.

If human clinical trials produce similar results, the research could point toward new approaches for treating Alzheimer’s disease, which affects an estimated 7.2 million people in the U.S. Still, Weaver cautioned that “it’s going to take a cocktail of drugs to treat Alzheimer’s disease. There’s not going to be a magic bullet.”