Targeting a specific blood vessel molecule may help to prevent the deadly spread of breast cancer around the body, research suggests.
The protein, endosialin, helps breast tumour cells to "escape" into the blood stream, a study has shown.
Detecting endosialin may in future provide a biomarker test for high-risk breast cancer, researchers said. Blocking the molecule with a drug could even help to prevent and contain the spread of breast cancer.
Endosialin is produced by pericytes, large spider-like cells that wrap around blood vessels and support their growth and function.
Early research showed that removing the protein from genetically engineered mice stopped breast cancer cells migrating into blood vessels.
A follow-up study of 334 women with breast cancer found that those with higher levels of endosialin were significantly more likely to experience metastasis, or cancer spread.
Professor Clare Isacke, from The Institute of Cancer Research in London, said: "Our study sheds valuable light on the role of pericytes - a type of cell that wraps around blood vessels - in helping breast cancer cells escape into the bloodstream and spread round the body.
"We found that a molecule called endosialin, which is produced on the surface of pericytes, plays a key role in aiding the getaway of cancer cells.
"We believe that endosialin could be a useful marker of how likely a woman's breast cancer is to spread around the body.
"And it might even be possible to block cancer spread by targeting this molecule with new drugs - something we plan to explore in future studies."
Each year advanced metastatic breast cancer kills 11,500 women and 80 men in the UK.
Baroness Delyth Morgan, chief executive of the charity Breast Cancer Now which part-funded the study, published in the journal Cancer Research, said: "This discovery paves the way for research that could help prevent and contain the spread of breast cancer.
"We're hopeful that this fundamental understanding could lead to new ways to identify patients at high risk of their breast cancer spreading, who could be offered more intensive treatment.
"That endosialin could also eventually be targeted by drugs to prevent and contain secondary breast cancer is a really exciting prospect."