The genetics underlying a smoker's risk of developing lung cancer has apparently been uncovered by British researchers.
Study leader Professor Richard Houlston has identified three areas of DNA that are linked to lung cancer risk in smokers.
Two of them also influence the type of cancer, which develops.
The research team found specific differences associated with lung cancer risk on chromosomes 5, 6 and 15.
It showed that people with genetic changes on chromosome 5 were more likely to develop a type of cancer called adenocarcinoma.
The region highlighted on chromosome 6 appears to influence whether a patient developed adenocarcinoma or another type called squamous cell carcinoma.
And two independent sites on chromosome 15 were found to have a role in whether or not a smoker develops lung cancer.
The researchers suggest that current or former smokers who carry one copy of each of these genetic variants increase their risk of lung cancer by 28pct.
The risk increases to 80pct in smokers who carry two copies of these genetic variants.
"The next step is to dig deeper to pinpoint which gene, or genes in these regions, cause the increased risk of developing lung cancer and how they actually trigger this increase," BBC News quoted Houlston as saying.
Dr Lesley Walker, director of cancer information at Cancer Research UK who partly funded the research, said smoking was responsible for the vast majority of lung cancers.
"This research shows that inherited genetic variation accounts for some of this risk and the type of lung cancer that develops," she said.
She added: "The best thing a smoker can do to reduce their risk of lung cancer, and a range of other life-threatening conditions, is to quit."
The findings appear in Cancer Research journal.