The team from the University of Texas and University of Cincinnati examined a region of chromosome 6q in a group of families in which several members had been affected by lung cancer.

Their study showed that people with high-risk genes on chromosome 6q had a 4.71-times higher risk of developing lung cancer, even if they had never smoked. Smokers with up to 20 pack-year histories had a risk 4.25-higher than non-smokers without high-risk genes.

However, the chances of those with the high-risk genes developing cancer did not rise substantially with increased smoking. Heavy smokers with high-risk genes had only a 23% higher risk of developing lung cancer than non-smokers with these genes.

The researchers stressed that, for those who carried the inherited risk and then smoked, it did not matter if they were light or heavy smokers, they were significantly more likely to develop lung cancer.

University of Cincinnati researcher Marshall Anderson said the results demonstrated the strong gene-environment interaction in lung cancer.

‘If you have a family history of lung cancer, you probably should not even be around cigarette smokers,' he said.