Some stress can be good for the body, helping fight off cancer, researchers reported on Thursday.
Experiments with mice showed that animals put into a stressful situation, even fighting with other mice, did a better job of fighting tumors than mice left to chill out.
They said their findings, published in the journal Cell, point to a possible neurological treatment for cancer.
"The way we live, and how we live, may well have a much bigger impact on the prognosis of cancer than we recognized previously," Dr. Matthew During, a professor of neuroscience who worked on the study, said in a telephone interview.
During's team injected mice with melanoma, a type of fast-growing skin cancer, and let the tumors grow. They put some of the mice in a large cage, with lots of toys, space and many more other mice than usual.
Other mice stayed in ordinary lab cages.
After three weeks, tumors shrank almost in half in the mice in the "stimulating" cage and they shrank 77 percent after six weeks. The tumors completely disappeared in 17 percent of the mice, with no other cancer treatment.
Tumors continued to grow in the other mice.
During believes that more than simple stimulation is at work in the mice. The mice in the "enriched" cages were a little stressed out.
"You find some of them with little bite marks and fight marks," said During. "It's not all friendly."
Although common wisdom holds that stress is not healthful, the body's response to stress is complex, and hormones released in response to stress can have positive effects.
To show the benefits were not simply due to exercise, the researchers placed running wheels in the smaller cage. The mice ran up to three times as far as the mice in the large cage, but were not more resistant to cancer.
Experiments to see what was happening biologically in the mice showed the stressed mice were producing more of a brain chemical called brain-derived neurotrophic factor.
This compound reduces the production of leptin, a hormone linked with appetite and also associated with melanoma, prostate and breast cancer. The more leptin the mice produced, the smaller their tumors were.
Leptin acts differently in mice than it does in humans, and cancer grows differently in mice injected with tumors than it does in people. But During believes the findings may nonetheless apply to people.
"The key is that we believe that this pathway that we've defined here exists in humans," he said.
"This suggests we can also start considering treating cancer by operating on the brain as well and introducing a gene to activate this pathway," he added.
Up to now, scientists have only studied mice in situations of severe stress. That mice do better in situations of moderate stress has implications for cancer patients, During said.
"We shouldn't be simply avoiding stress and looking for happiness," During said. "We should be getting involved in team sports, getting involved in social groups, where there's sort of an interactive dynamics which are a little bit challenging for us." (Reuters health/Emma Ashburn)
SOURCE: http://link.reuters.com/jur56m Cell, July 9, 2010.