Tumors Shrink When Mice Live in Stimulating Environments

New research has found that mice with cancer are better able to fight off the disease when they are in complex, stimulating environments, with lots of toys and other mice that they interact - and compete - with. Although this was an animal study, the scientist behind it thinks it could signal new ways of treating cancer in people.

The study involved genetically-identical mice with cancerous tumors. Some mice were put in standard laboratory cages, in groups of five or so, with plenty of food and water. Another group lived in what the researchers call an enriched environment up to 20 mice per cage, with toys, hiding places, and running wheels.

"And what was surprising to us was that [in] the animals in the enriched environment, the cancers are 40 percent smaller" after just three weeks, said lead author Matthew During of Ohio State University. "When we moved that enrichment to six weeks, now, the cancers were approximately 80 percent smaller - a dramatic effect, and not only that, but 17 percent of those animals had no tumors whatsoever."

It took several years of further experiments and analysis, but During and his colleagues ultimately concluded that the mild stress of all that activity and interaction activated a communication channel that prompts fat cells to stop releasing a hormone called leptin, which accelerates cancer growth.

"The crux of what this study is all about is that we define a new pathway where the brain talks to fat," he said. "And the brain is activated by this challenging environment and signals to the fat to stop the release of this hormone. And this particular hormone stimulates and feeds the cancer growth, essentially. And that's the simplest analysis of what we showed."

During's field is gene therapy, so he's working on a way to recreate that effect by modifying the gene that controls the leptin hormone. But the study also suggests a more low-tech solution might be helpful.

"Being more socially engaged in your community - maybe in environments which aren't always just the same, a little bit more challenging socially - may be a very good thing. So I think this study gives investigators who are working with cancer survivors some ideas as to how best, perhaps, to think about prescribing a lifestyle," said the scientist.

Matthew During's paper on how the mild stress of an enriched environment can change the production of hormones related to cancer growth is published in the journal "Cell."