Stressed mice grew larger tumours
Social isolation may make cancer more deadly, US research on mice suggests.
Researchers found the social environment can modify the biology of the disease - and lead to significant differences in outcome.
Female mice stressed because they were separated from their mothers developed more and larger mammary gland tumours than more contented animals.
The University of Chicago study appears in the journal Cancer Prevention Research.
Previous research has suggested that social support can improve health outcomes for patients with breast cancer, while social isolation has been linked to an increased risk of death from several chronic diseases.
The Chicago team worked with mice genetically predisposed to mammary gland cancer.
They found changes in the activity of genes that play a role in tumour growth in the stressed animals, suggesting that they may have been directly influenced by surging levels of stress hormones.
The researchers said more work was needed to pin down exactly which cell types are affected.
But researcher Dr Suzanne Conzen said the study raised hopes of new ways to block cancer growth.
She said: "Given the increased knowledge of the human genome we can begin to objectively identify and dissect the specific alterations that take place in cancer-prone tissues of individuals in at-risk environments and that will help us to better understand and implement cancer prevention strategies."
Dr Caryn Lerman, editor of the journal, said: "This study uses an elegant preclinical model and shows that social isolation alters expression of genes important in mammary gland tumour growth."
Professor Thea Tlsty, of University of California San Francisco, said it had long been known that psychological factors could influence disease, but not how.
She said the study added to growing evidence that chemicals circulating in the blood - such as stress hormones - could influence the development of cancer by turning genes on and off within cells with the potential to turn malignant.
Previous work has also suggested that depression can have a negative effect on cancer prognosis.
Oliver Childs, of the charity Cancer Research UK, warned against drawing any firm conclusions.
He said: "These experiments were carried out in mice, so certainly do not prove that the stress caused by social isolation causes cancer to get worse in humans.
"It is now widely recognised that stress plays a part in illness, but no-one really knows how much and there is no good evidence from controlled studies that stress contributes to cancer progression."