A smoker's risk of developing lung cancer increases doubly in the presence of a notorious breast cancer gene, shown in a study on Sunday.
The finding, published in the journal Nature Genetics, opens possible avenues for treatment and for screening of those at risk, said the authors.
"Our findings provide further evidence for inherited genetic susceptibility to lung cancer," they wrote.
"All smokers are taking a considerable risk with their health, regardless of their genetic profile, but the odds are stacked even more heavily against those with this genetic defect," added Paul Workman, deputy chief executive of the Institute of Cancer Research (ICR), which took part in the study.
A meta-analysis of four studies found that about a quarter of smokers with a specific defect in the BRCA2 gene will develop lung cancer in their lifetime, compared to 13 percent of the general smoking population.
The analysis had compared the DNA of 11,348 people with lung cancer to those of 15,861 without.
"The link between lung cancer and defective BRCA2, known to increase the risk of breast, ovarian and other cancer, was particularly strong in patients with the most common lung cancer sub-type, called squamous cell lung cancer," said a statement from the ICR.
- Strongest genetic link -
Other genes have been linked to lung cancer risk before, but the role of BRCA2 was unknown.
The defective variant, carried by about two percent of the population, "is the strongest genetic association with lung cancer reported so far," the study authors said.
The research also threw up a second, new gene, CHEK2, which plays a smaller role in lung cancer risk.
"The results suggest that in the future, patients with squamous cell lung cancer could benefit from drugs specifically designed to be effective in cancers with BRCA mutations," said the ICR.
"A family of drugs called PARP inhibitors have shown success in clinical trials in breast and ovarian cancer patients with BRCA mutations, although it is not known whether they could be effective in lung cancer."
All the study subjects were of European descent, and it was not clear if the findings would apply to other groups, the authors said.
The BRCA1 and BRCA2 (for BReast CAncer susceptibility) genes are the best-known inherited cause for breast cancer.
Last year, Hollywood star Angelina Jolie announced she had had both breasts surgically removed as a preventative measure after tests revealed she carried the specific BRCA mutation, despite not having been diagnosed with cancer.
The main cause of lung cancer is smoking, although genetics are known to increase the risk.
According to the International Agency for Research on Cancer, lung cancer is the most common cause of death from cancer -- estimated to be responsible for nearly one in five, or 1.59 million, deaths in 2012.
It is the most common type of cancer, with an estimated 1.8 million new cases in 2012.
"We know that the single biggest thing we can do to reduce death rates is to persuade people not to smoke, and our new findings make plain that this is even more critical in people with an underlying genetic risk," said study leader Richard Houlston.