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Isolation and stress identified as contributing to breast cancer risk - EurekAlert (article link)

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- The researchers found that isolation and stress result in a 3.3-fold increase in the risk of developing cancer among rats with naturally occurring mammary tumors.
- The researchers further found that rats living in isolation experienced a 135 percent increase in the number of tumors and a more than 8,000 percent increase in their size.
- The research establishes, for the first time, that isolation and stress could be a factor in human breast cancer risk

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The research establishes, for the first time, that isolation and stress could be a factor in human breast cancer risk, said Martha McClintock, a psychologist at the University of Chicago and an author of a paper in current issue of the Proceedings of the National Academy of Sciences.

Researchers at the University have been studying social isolation in the context of breast cancer development after having found that that many women living in high-crime neighborhoods must deal with a variety of stressors, including social isolation. In particular, African American women have been noted to have an earlier onset of breast cancer, although total incidence is similar to women from other ancestries.

The results of the study are published in a PNAS paper titled, "Social Isolation Dysregulates Endocrine and Behavioral Stress While Increasing Malignant Burden of Spontaneous Mammary Tumors."

The study published in PNAS found that isolation led to a higher production of a stress hormone, corticosterone, among rats that were kept alone and subjected to the disturbances of colony life as well as stressful situations, such as the smell of a predator or being briefly constrained. Additionally, the isolated rats took longer to recover from a stressful situation than rats that lived together in small groups.

The study also suggests a causal relationship between social interaction and disease by showing that living alone first causes rats to have higher stress hormones, beginning in young adulthood, become fearful, anxious and vigilant and then prone to malignancy in late-middle age. The study further showed that the stress hormone receptor entered the nucleus of mammary tumor cells in isolated rats, where gene regulation occurs, something that happened less often in the cells of the non-isolated rats.

The researchers further found that rats living in isolation experienced a 135 percent increase in the number of tumors and a more than 8,000 percent increase in their size. The impact of isolation was much larger than the impact another environmental source of tumor formation—the unlimited availability of high-energy food.

In natural situations, estrogen and progesterone produced from ovaries play a role in the majority of naturally occurring mammary and breast cancers tumors. In the rat study, tumors naturally developed in late middle age, while ovaries were no longer fully functioning, further suggesting the role of isolation and stress hormones in cancer development.

http://www.eurekalert.org/pub_releases/2009-12/uoc-ias120309.php