A simple breath test could reveal lung cancer in its earliest, more treatable stages.

Researchers at the Cleveland Clinic in the U.S. have developed a test that uses a chemical sensor to detect a chemical signature in the breath of people with lung cancer.

Every year, 22,000 Canadians contract the disease, but by the time symptoms emerge, it's usually too late to treat, which is why 95 per cent of patients don't survive.

Doctors hope early screening may increase survival rates.

The quarter-sized sensor, which changes colour, was able to accurately predict the presence of cancer in nearly three of four people, the team reports in the online issue of the journal Thorax.

"Ultimately, this line of investigation could lead to an inexpensive, non-invasive screening or diagnostic test for lung cancer," they concluded.

The sensor is designed to pick up on metabolic changes in lung cancer cells that cause volatile organic compounds to be exhaled. Until now, scientists have used expensive laboratory equipment to detect the compounds.

Investigators tested the sensor on 122 people with different respiratory diseases, including 49 people with small cell lung cancer at various stages of development, as well as 21 healthy people.

Age, gender and stage of disease did not affect the results.

More tests are needed before the sensor becomes commercially available. 

Researchers are also looking at whether annual CT scans could help detect lung cancer earlier in smokers and other people at high risk for the disease.