Scientists are studying a way of blocking the movement of cancer cells around the body, which could halt the creation of lethal tumours.

An answer to a long-standing cancer riddle could lead to new ways of blocking metastasis, a potentially lethal tumour spreading around the body.

Scientists found that "free floating" cancer cells are able to survive because of surface proteins called integrins that normally keep tumours anchored to one place.

The molecules switch roles and pair up with another protein to send out signals that keep the cells alive and dangerous.

Blocking the movement of integrins from outside to inside cancer cells could provide a new strategy for combating metastasis, the researchers believe.

Cancer patients are most often killed by splinters of their original tumour seeding secondary growths in vital organs, such as the liver.

Metastasis has been a puzzle to scientists because a cancer cell that "goes solo" and leaves the protective environment of an established tumour would normally be expected to die.

The researchers, whose findings are published in the journal Nature Communications, investigated the mystery in cell cultures, zebra fish and mice.

Lead scientist Dr Stephanie Kermorgant, from Queen Mary University of London, said: "Metastasis is currently incurable and remains one of the key targets of cancer research.

"Our research advances the knowledge of how two key molecules communicate and work together to help cancer cells survive during metastasis. We're hoping that this might lead to the discovery of new drugs to block the spread of cancer within the body."

Integrins are signalling molecules that help cancer cells attach themselves to their surroundings.

Their role in metastasis was discovered when scientists showed how they teamed up with another protein, called c-Met.

The pair move inside the free-floating cancer cell to a specific location where they send out their survival signals.

Metastasis was less likely to occur when the molecules were prevented from entering the cell or travelling to their destination within it, the scientists found. They conducted the experiments using both breast and lung cells.

Drugs already exist that inhibit integrins, but these only target their adhesive function. This could be one reason for their limited success, according to the researchers.

An alternative approach might be to stop integrins entering cancer cells, they said.