Scientists have identified genetic variations that raise the risk of lung cancer for smokers and former smokers.
There is some evidence to suggest that the variations may make carriers who smoke more addicted to tobacco.
The variants are common in the population – but they only raise lung cancer risk in those who have smoked.
Current or former smokers who carry two copies of both variants, one from each parent – about 15% of the total – have a raised risk of 70-80%.
Those who carry one copy of each variant have a raised risk of around 28%.
All the researchers agree the work is a major stop forward in identifying people at risk for non-small cell lung cancer – which makes up 80% of all lung cancer cases.