Professor John Field of the Roy Castle centre discusses the findings

Researchers at the Roy Castle International Centre for Lung Cancer Research in Liverpool say the discovery could help to identify those most at risk from the disease.

The breakthrough could - in the long term - lead to a screening programme similar to that for breast and cervical cancer.

The findings, published on Tuesday in the Cancer Research Journal, are part of a major 10-year project looking at Liverpool's high incidence of lung cancer.

The city has the highest number of people with lung cancer anywhere in England and Wales.

Figures for lung cancer among women in the city are way above the national average, with lung cancer now a more common cause of death among women on Merseyside than breast cancer.

Scientists have discovered that genetic markers in fluid taken from the lungs of lung cancer patients were also present in fluid taken from the lungs of a number of individuals without the disease.

The second group of individuals will be closely monitored to see whether or not they develop cancer.

Deadly disease

In Britain 42,000 people are diagnosed with lung cancer each year and 50% will be dead within four months because the disease has already progressed too far. The five-year survival rate is only five in 100.

However, most lung cancer deaths are preventable if the disease is diagnosed at an early stage.

Currently the only way to diagnose lung cancer is with invasive techniques, such as taking a sample of flesh or cells from the inside of the lung for analysis. By the time a diagnosis is made, the disease is often untreatable.

The institute scientists are working on a non-invasive test using a nebuliser-inhaler. The patient breathes in a saline mist which induces a cough.

Scientists can then analyse the sputum.

But Professor John Field, director of the Centre, said medics were still years away from an early detection system for the disease and a national screening programme.

But he said the results of preliminary work were very encouraging.

Common malignancy

Prof Field said: "Lung cancer is the most common malignancy in men in the UK.

"Sadly, many patients have progressed to advanced disease before their tumours are detected by conventional diagnostic techniques.

"The presence of the same genetic markers in material obtained from the lungs of cancer patients and from the lungs of people who are not cancer patients suggest that a combination of sophisticated genetic techniques and a non-invasive examination in a health centre, could identify individuals who are at risk of developing the disease.

"Early identification of such individuals would greatly improve the effectiveness of treatment."

The Liverpool Lung Project is one of the largest population-based studies in lung cancer in the world.

It is monitoring a selected group of 7,500 individuals on Merseyside between 1998 and 2008.

The aim of the project is to use genetic techniques in conjunction with lifestyle data to identify individuals who are at risk of developing the disease.