The results of the US study test was published in the international journal of respiratory medicine Thorax.

In the tests, the colour testing device, which is the size of a coin and is surprisingly inexpensive, had a 75 per cent success rate in detecting people with different cancers.

However, the tests were not 100 per cent accurate. The device showed false positives on people who did not have lung cancer. This reduces the device's effectiveness removing doctor's ability to start immediate treatments.

The technique called a "colorimetric sensor array" picks up the chemical fingerprint of the breath of people with lung cancer that are caused by the tumours.

Cancers produce volatile organic compounds (VOCs) that are different from normal cells. Tumours in the lungs are more likely to contain increased signs of these abnormal compounds. This increases the potential for the device to pick up a lung cancer "fingerprint" in the breath.

Surprisingly, dogs are able to detect VOCs and differentiate between people with lung cancer and healthy people. With 'early response' a major factor in survival rates, there are many who wonder why dogs are not trained to detect VOCs in the same manner that dogs are trained to detect drugs and other compounds.

The prototype of this device was developed by Dr Peter Mazzone of the The Cleveland Clinic in Ohio in collaboration with the private company ChemSensing of Champaign, Illinois. The private company customizes Metalloporphyrins, a chemically reactive dye family that are sensitive to VOCs.

They are working to develop an inexpensive device. The only equipment available to the public are mass spectrometers or gas chromatographs. These are expensive and require the services of an expert to analyse the results.

The new device resembles a 2 cm square key fob with a 6 by 6 pattern of coloured dots visible through the plastic casing. Changes in the pattern of the dots indicate the presence of VOCs in the breath based on the gas makeup of the breath.

Scientists tested 143 patients. Patients needed to breathe into the device for 12 minutes. The test group was divided into three groups. Some patients had lung cancer at various stages, some had other forms of respiratory illnesses like emphysema. The rest were healthy.

The device spotted 73 per cent of the lung cancer patients and cleared 72 per cent of the non-lung cancer patients. This is not 100 per cent, but the results are acceptable.

The US National Cancer Institute reports that lung cancer is the second most common cancer and the most common cause of cancer-related deaths in the US, with more than 200,000 new cases diagnosed, and 160,000 plus deaths due to the disease each year.

The World Health Organization (WHO) estimates that the global annual death rate from lung cancer at 1.3 million.