A single protein may hold the key to turning the tide on lung cancer - still the world’s biggest cancer killer - research published on Tuesday shows.

Researchers at Vanderbilt University in Nashville found that type 2 receptors for Transforming Growth Factor-b - a family of proteins that controls key functions such as cell growth and death - were missing in non-small cell lung cancer victims.

A check on mice injected with lung cancer cells confirmed the findings, with much smaller and less aggressive tumours developing in those carrying the type 2 TGF-b receptors.

“We’ve established for the first time that these important molecules are either missing or that their action is reduced in three-quarters of all cases of lung cancer,” said lead researcher Professor Pran Datta.

“When we restored the molecules in lung cancer cells in mice, they reduced the ability of the cells to grow as tumours,” he wrote in the British Journal of Cancer.

Having established the link, researchers must now find out how or why the key receptor molecules go missing as the disease develops, in order to find a way of treating it.

Some 80 percent of lung cancers are non-small cell lung cancers, and the overwhelming cause of lung cancer is smoking - either active or passive.