“Lonely women could be at greater risk of breast cancer,” the Daily Mail reported. It said that scientists have found that the stress and anxiety caused by social isolation can speed up the growth of cancers.
The news story is based on a laboratory study in genetically engineered mice and the results cannot be directly applied to humans. Although animal studies can be valuable for gaining a general understanding of how diseases develop, humans have a very different biology from mice. These findings cannot be interpreted to mean that being sociable protects you against breast cancer or any other cancer, or that being unsociable raises your risk, or gives you a worse prognosis or outlook.
Where did the story come from?
The research was carried out by J Bradley Williams and colleagues from The University of Chicago. It was funded by the National Institute of Health Centers for Population Health and Health Disparities, the University of Chicago Cancer Center's Women's Auxiliary Board, and a University of Chicago Cancer Center core grant. It was published in the peer-reviewed medical journal Cancer Prevention Research .
What kind of scientific study was this?
This study investigated how an unfavourable social environment affects the body at a molecular and cellular level and examined the role of genetics and the environment in the development of cancers. Previous research has suggested that social support improves the outcomes (outlook) for people with cancer, and social isolation has the opposite effect.
Studies in rats also show that socially isolated animals have higher levels of the stress hormone corticosterone. Other studies in female rats found that less sociable female rats developed mammary gland tumours earlier than sociable rats.
This experiment involved a group of genetically engineered mice that were predisposed to developing mammary tumours. Some of the mice were housed together in groups of four and others were housed alone. Throughout the animals' lifespan, and after they died at between 15 to 20 weeks, researchers repeatedly measured the size of the mammary gland tumour, the tumour differentiation, gene expression, corticosterone levels (taken from blood sampling), and behaviour of the mouse.
The purpose of this was to investigate the precise molecular consequences of an "unfavourable social environment". Researchers were particularly interested in how the mammary gland was affected.
What were the results of the study?
Overall, tumour incidence was higher in the isolated group (80.8% of isolated mice compared to 65.4% of social mice), and the mice that were housed alone developed tumours that were of a larger size (61.5% of isolated mice compared with 30.8%).
The tumours in the isolated mice were also more likely to be poorly differentiated (made up of cancer cells that are very unlike normal healthy cells, meaning the cancer is likely to be more serious). Gene expression in the mammary glands was more likely to have changed in genes relating to immunologic (immune system) and inflammatory disease, fat breakdown, and genes coding for key enzymes involved in cancer development.
As expected, isolated mice were found to have heightened corticosterone levels and altered behaviour (they were less likely to leave their home and move into an open area).
What interpretations did the researchers draw from these results?
The researchers conclude that they have used a mouse model of human breast cancer and found that a chronically isolated social environment correlates with alteration of mammary gland gene expression. They say the differences in the cancers that developed in the two groups suggests that isolation may activate key cancer-linked metabolic pathways (a series of chemical reactions within a cell).
What does the NHS Knowledge Service make of this study?
This research was done on genetically engineered mice that were predisposed to developing mammary gland tumours. The work is valuable in understanding how environmental change may have an effect on the biological development of tumours but humans are very different from genetically engineered mice.
As the researchers say, their work provides “a new framework with which to begin to evaluate the molecular mechanisms whereby an adverse social environment may be associated with changes in breast cancer biology”.
However, this is all that can be concluded from this research at present. It does not mean that being sociable protects against breast cancer or any other cancer, or that being unsociable raises your risk or has any difference on prognosis or outlook.