Stress can hasten the spread of breast cancer to the bones, research suggests.
Studies of mice showed that responses to stress made it easier for tumours to take root in the bone.
By dampening down part of the body's "fight or flight" mechanism, scientists were able to prevent the cancer invasion.
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The findings raise the possibility of common drugs called beta-blockers being used to prevent the potentially lethal migration of breast cancer to the bone.
Beta-blockers are normally used to treat angina chest pains, irregular heart beat, and high blood pressure.
Dr Florent Elefteriou, director of the Centre for Bone Biology at Vanderbilt University in the US, said: "If something as simple as a beta blocker could prevent cancer metastasis to bone, this would impact the treatment of millions of patients worldwide."
Previous research had shown that the sympathetic nervous system, which plays a key role in the "fight-or-flight" response to stress, can stimulate bone remodelling.
It also employed some of the same signalling molecules implicated in breast cancer bone metastasis.
"We came to the hypothesis that sympathetic activation might remodel the bone environment and make it more favourable for cancer cells to metastasise there," said Dr Elefteriou.
Clinical evidence showed that breast cancer patients suffering from stress or depression after their initial treatment had shorter survival times.
To test the theory, the scientists traced human breast cancer cells bearing fluorescent "tags" that they injected into the hearts of mice.
When the mice were given a drug that mimicked sympathetic nervous system activation, more cancer cells travelling through the bloodstream established tumours in the bones.
Mice that were stressed by being physically restrained showed the same response.
Treating the stressed mice with propranolol, a type of beta blocker, reduced the number of bone lesions.
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The research appears in the online journal Public Library of Science Biology.
Sympathetic nervous system activation increased bone levels of a signalling molecule called RANKL, said the scientists.
RANKL is known to promote the formation of osteoclasts, cells that break down bone tissue. It is also involved in cell migration.
Dr Elefteriou's team showed that the transport of breast cancer cells to the bones depended on RANKL.
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