(HealthDay News) -- While smoking is far and away the biggest risk factor for lung cancer, having a close relative who has been diagnosed with the disease nearly doubles your risk of developing the deadly disease.
A new study in the October issue of Chest found that people with a first-degree relative -- that means mother, father or sibling -- who had lung cancer had a 95 percent higher risk of developing the disease themselves.
"Our long-term follow-up of a large-scale, population-based cohort identified a significant increase in the risk of lung cancer associated with a family history of lung cancer in a first-degree relative in a Japanese population," the study authors wrote.
Dr. Jay Brooks, chairman of hematology and oncology at the Ochsner Clinic Health System in Baton Rouge, La., said this study confirms what's already known about family history and the risk of lung cancer, and that "it's an important thing for physicians to realize."
"As a clinician, when I have someone with lung cancer, I ask the family members, 'Who smokes cigarettes?' Then I explain that they have a two- to three-fold higher risk of lung cancer because of their family history, and this is just another reason to quit smoking because they have a genetic susceptibility to the carcinogens in tobacco," explained Brooks.
The U.S. Centers for Disease Control and Prevention estimates that more than 180,000 new cases of lung cancer are diagnosed each year in the United States, and nearly 170,000 Americans die from the disease annually. It's the second leading cause of death for men and the third leading cause of death for women, according to the CDC. Cigarette smoking is the most common cause of the disease, according to the National Institutes of Health, though not everyone who gets lung cancer is a smoker or former smoker.
The current study followed more than 102,000 middle-aged and older Japanese adults for as long as 13 years; there were more women (53,421) than men (48,834). During the study period, 791 cases of lung cancer were diagnosed.
The researchers found that having a first-degree relative with lung cancer nearly doubled the odds of developing lung cancer. The association was even stronger for women. Women who had a first-degree relative with lung cancer almost had triple the risk of lung cancer, while men with a first-degree relative with lung cancer had about a 70 percent higher risk.
Additionally, people who had never smoked had a higher risk of developing lung cancer themselves if they had a first-degree relative with the disease than did smokers with close family members with lung cancer.
Family history was also more strongly associated with a particular type of lung cancer -- squamous cell carcinoma.
Brooks and Dr. Ann G. Schwartz, who wrote an accompanying editorial in the same issue of the journal, both said it wasn't clear why family history would confer a greater risk for women than for men. Schwartz said one possibility is that women are more familiar with their family histories and may just be reporting family history more accurately. Brooks also pointed out that this finding might only apply to Japanese women and not other populations.
It's also not clear exactly why family history is associated with a greater risk for those who never smoked, though Schwartz said it may have something to do with different lung cancer types. It's possible that the type of lung cancer nonsmokers often get may also be one where the genetic susceptibility is passed from generation to generation.
While there aren't clear-cut screening guidelines in place for someone with a family history of lung cancer, Schwartz said, "You need to make your physician aware of your family history; don't discount it."
She added that she'd like to see people with a family history of the disease identified as high-risk for lung cancer and included in screening studies.
"If you have a family history of lung cancer, you have a genetic susceptibility to the carcinogens in directly inhaled and in secondhand tobacco smoke. Avoid all exposure to tobacco, quit smoking if you're a smoker," and don't let your children be exposed to tobacco smoke, Brooks said.
To learn what steps you can take to help prevent lung cancer, visit the National Cancer Institute.