Sept. 29 (HealthDay News) -- A socially isolated, stressful environment can speed up the growth of breast cancer, researchers studying the effects of stress in animal models reported Tuesday.

Social isolation can actually change the expression of genes important in the growth of mammary gland tumors, according to Dr. Suzanne D. Conzen, an associate professor of medicine at the University of Chicago and the study's lead author.

"As far as we know, this is the first assessment of gene expression in mammary glands, looking at the molecular basis for differences in tumor development under the setting of social stress," Conzen said at a news conference Tuesday.

The findings, published in the October issue of Cancer Prevention Research, follow other studies, some in humans, that showed stress can adversely impact cancer. One study, for instance, found that stressful marriages are bad for breast cancer recovery.

Conzen and her colleagues randomly assigned mice that were genetically susceptible to breast cancer to live either in isolation or in group housing.

"We separated the mice at a very young age, just a few days after they had been weaned from their mothers' milk," Conzen said. "Mice are social animals. In the wild, they live in groups of three or four. They have dramatic responses to isolation."

"What we found was the isolated mice developed larger and more breast cancers than the group-housed mice," she added.

Three and a half weeks into the isolation, Conzen's team measured gene expression in the animals' mammary glands, the equivalent of the human breast. "We found very reproducible changes in gene expression [in the isolated mice]. We found genes that were turned on and turned off that had to do with metabolism," she said. These pathways are known to contribute to increased growth of breast cancer, she added.

The isolated mice also had a higher corticosterone stress hormone response than did the group-housed mice.

The changes in the expression levels of metabolic pathway genes occurred in the isolated mice even before the tumor size differences were able to be measured, Conzen said.

So what are the practical applications of the research?

The findings may suggest molecular biomarkers, or targets, for preventive intervention in breast cancer, she said.

"Many questions remain," Conzen added. "One of the things we did note is that the isolated animals were much more vigilant, less exploratory. They released more of a stress hormone when we added another stressor to the situation [besides the isolation]."

Thea Tisty, a pathology professor at the University of California, San Francisco, who is familiar with the findings, called the research "a very exciting beginning."

The implication is that perceived or actual stress from outside can affect which genes get turned on or off. If the research findings bear out, it could lead to a way to catch tumors in their formation before they become tumors and suppress them, she said.

Another expert speaking at the briefing cautioned that the findings, while exciting, are only preliminary and based only on animal studies.

"This is an area that has a long way to go in terms of understanding how these factors play out in humans," said Caryn Lerman, the Mary W. Calkins Professor of Psychiatry at the Abramson Cancer Center at the University of Pennsylvania in Philadelphia.

SOURCES: Suzanne D. Conzen, M.D., associate professor of medicine, Ben May Department for Cancer Research, University of Chicago; Thea Tisty, Ph.D., professor of pathology, University of California, San Francisco; Caryn Lerman, Ph.D., Mary W. Calkins Professor of Psychiatry, Abramson Cancer Center, University of Pennsylvania, Philadelphia; October, 2009 Cancer Prevention Research