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Scientists say they have developed a breath-test that can accurately tell if a person has bowel cancer.

The test, which looks for exhaled chemicals linked to tumour activity, was able to identify a majority of patients with the disease.

The British Journal of Surgery reported an overall accuracy of 76%.

However, another scientist said it was unlikely a fully functioning and reliable breath-test would be available soon for the general public.

Scientists are working on breath-tests for a host of other diseases, including several types of cancer, TB and diabetes.

If diagnosed and treated early, the chances of stopping cancer can be good, but there is often little or no outward sign of the disease until it has progressed significantly.

The current screening test for bowel cancer looks for signs of blood in the faeces, but only a small proportion of those who test positive actually have colorectal cancer, which means unnecessary and invasive further testing for many people.

The breath-test technology relies on the idea that the biology of tumours can lead to the production of specific "volatile organic compounds", combinations of chemicals unlikely in a healthy person.

These can be found in small amounts in the breath of the patient, and early studies found dogs could be trained to identify them - although the latest study relies an electronic device to analyse breath gases.

The team from a hospital in Bari, southern Italy, compared the breath of 37 patients known to have bowel cancer with that of 41 "controls" who were thought to be healthy.

The initial test identified the cancer patients with 85% accuracy, and although, when combined with a follow-up test, the overall result fell to 76%, the researchers were upbeat about its potential.

"The present findings further support the value of breath-testing as a screening tool," they say.

It might be possible that the technique could help identify patients whose cancer was returning after treatment.

Bigger studies with a greater number of patients were now needed to fine-tune the test and confirm it worked, said Dr Donato Altomare and colleagues.

Breath-tests have been suggested for a variety of diseases, including other types of cancer, TB and diabetes, but Dr Claire Turner, a lecturer in analytical chemistry at the Open University, said that it was often difficult to interpret the cocktail of chemicals contained in every breath, as they could be influenced by what the patient had been eating, or even just by being ill or spending time in a hospital environment.

She said: "These technologies show a great deal of promise, and hopefully we will see larger studies in the future.

"However, we are unlikely to see this kind of breath testing available widely in the short term."