Nerves and stress help to trigger and drive prostate cancer, new research suggests.
Branches of the nervous system that control involuntary functions may play important roles in the disease, scientists have discovered.
The research also points to stress, and the body's response to it, being a possible risk factor for prostate cancer.
In addition it indicates a potential new treatment pathway involving drugs such as beta-blockers, already used to lower blood pressure.
Previous work has shown that some tumours grow and migrate along nerve fibres. Nerves are commonly found in and around tumours, but their role in cancer development has not been clear.
The new study, conducted both on mice and human tissue samples, focused on the autonomic nervous system which governs "automatic" functions such as heart beat and digestion.
Scientists in the US found that both branches of the autonomic nervous system appear to have important cancer-promoting effects.
One branch, the sympathetic nervous system (SNS), regulates the body's rapid "flight-or-fight" responses to stress and danger, for instance, by revving up heart rate and constricting blood vessels. The other, the parasympathetic nervous system (PNS), works in opposition to it, helping the body to relax, "rest and digest", and conserve energy when life is calmer.
The SNS fuels early phases of prostate cancer while the PNS becomes involved later when the disease spreads, the research showed.
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Stress comes into the picture because the study, published in the journal Science, revealed how the SNS promotes tumour growth by generating the neurochemical noradrenaline.
Like its close cousin adrenaline, noradrenaline is a primary stress hormone that prepares the body to meet threats by making it more aroused and responsive, shifting blood from the skin to the muscles, and raising heart rate.
The hormone binds to receptor molecules on the surfaces of tumour cells, triggering a cancer-stimulating biochemical response.
PNS nerve fibres release a different chemical that activates a signalling pathway in the connective tissue surrounding tumour cells, helping the cells to break away and invade other parts of the body.
Drugs for high blood pressure and anxiety called beta-blockers work by blocking noradrenaline receptors.
This may explain recent findings of improved survival in prostate cancer patients on beta-blockers, said the scientists.
"Although further studies will be required to dissect the molecular events linking tumour neurogenesis to cancer progression, our data raises the tantalising possibility that drugs targeting both branches of the autonomic nervous system may be useful therapeutics for prostate cancer," they wrote.
Analysis of tissue samples taken from prostate cancer patients showed that aggressive tumours had more nerve fibres within and surrounding them than non-aggressive tumours.
Tumour nerve density may provide the basis of a test for aggressiveness that could help doctors decide on best treatments for their patients, said the researchers.
Whether or not the findings apply to other forms of cancer is still uncertain.
"Clinical studies show that breast cancer patients who took beta-blockers did better than those who were not taking beta-blockers," said lead scientist Dr Paul Frenette, from the Albert Einstein College of Medicine in New York City. "This suggests that the same mechanisms are involved, but that remains to be seen."
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