A UK company is marketing a genetic test aimed at predicting the risk of smokers developing lung cancer. The test, known as Respirigene, assesses 20 different genetic markers which have previously been linked to lung cancer in combination with other known risk factors for the disease, such as age, any prior medical history of chronic lung disease, and family history of lung cancer, to decide whether an individual is in a high, moderate or low risk category for lung cancer.

Lab 21, the company who markets the test in New Zealand and now the UK, asserts that the test acts as a powerful motivator to help people quit smoking and that it flags up those who could benefit most from regular cancer screening. But experts have expressed concerns about the scientific validity of the test, as well as the psychological implications of finding out this kind of information.

Paul Pharoah, a genetic epidemiologist at the University of Cambridge admitted he had serious doubts about the scientific validity of the test.' Very large genome-wide studies on tens of thousands of people have shown up at most five reliable genetic markers,' he told The Times newspaper.

In an accompanying commentary, Mark Henderson, science editor of The Times, questioned whether smokers were better off quitting regardless of the test's results, particularly considered the long list of other life-threatening health problems linked to smoking, including mouth and throat cancers, heart disease and strokes.

He said: ' As Respiragene points out, even those who get the lowest score on its test are almost 20 times more likely to get lung cancer than non-smokers. It is hard to escape the conclusion that £300 would be better invested in nicotine gum.'

Writing in response to the article in The Times science blog, Berwyn Clarke, chief scientific officer of Lab 21 Limited, rejected the claim that many of the genetic markers, known also as 'single nucleotide polymorphisms' (SNPs), have yet to be conclusively linked to lung cancer.

He said: ' Many of the additional SNPs used in the Respiragene lung cancer panel are related to a predisposition to COPD (chronic obtrusive pulmonary disease or emphysema). This was shown in a study published in 2008 (and supported by others). The genome-wide studies have made no allowance for this contribution of COPD-related genes to lung cancer and therefore have failed to identify them. This is why only 3-5 genes have been identified to date in these studies.'

While Clarke firmly believes that the test 'can provide impetus for smokers to quit smoking,' Peter Farndon, director of the National Genetics Education and Development Centre, warned that the test might actually provoke the opposite response, triggering a sense of fatalism among those delivered a 'high risk' prognosis and a sense of false security among those assigned to a 'low risk' one. 'People's psychological responses can be very unpredictable,' he warned.