When it comes to smoking and lung cancer risk, men and women are not created equal.

New research shows that women who smoke are twice as likely to develop lung cancer as men. However, they are half as likely to die when their disease is diagnosed early.

The international study included about 7,500 female and 9,400 male smokers or former smokers who were screened for lung cancer.

The findings confirm long-suspected gender differences in lung cancer incidence and outcomes among smokers. But it is not clear why men and women with the same smoking histories have different risks, says Cornell University’s Claudia Henschke, PhD, MD, who worked on the study.

“Women with lung cancer survive more often than men, but women also have twice the risk of getting lung cancer,” she tells WebMD. “And you don’t want to get this disease.”

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Men vs. Women

In the study, lung cancer incidence and outcomes were compared for male and female smokers and former smokers screened for the disease between 1993 and 2005.

None of the study participants had symptoms indicating the presence of lung cancer, such as persistent cough or shortness of breath.

But lung cancer was detected in 156 women, or 2% of those screened, and in 113 men, or slightly more than 1% of men in the study. Of those with cancer, 89% of the women and 80% of the men had early stage disease. Ninety percent of the women and 88% of the men had surgery to remove their tumors.

After controlling for the amount and years of smoking, disease stage, and tumor type, researchers found that women with lung cancer were roughly half as likely to die of their mostly early-stage disease as men.

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More Curable or Less Malignant?

The researchers say it’s not clear if the survival difference is due to the women having a more curable disease, or a less malignant one.

Other studies have shown that women with later-stage disease tend to respond better to chemotherapy and survive longer than men, lung cancer specialist Joan Schiller, MD, tells WebMD.

Schiller is president of the National Lung Cancer Partnership, which she founded to raise awareness about lung cancer in women and the importance of treatment.

Many people are surprised to learn lung cancer is not only treatable, but curable, when detected early, Schiller says. Most lung cancer patients have later-stage disease when diagnosed.

Investigators like Henschke and her colleagues are now studying the value of routine screening with computed tomographic (CT) X-ray imaging.

“One of the things that we see way too much of is patients coming to us much later than they should,” Schiller tells WebMD.

Anyone with persistent pulmonary symptoms that do not go away with treatment -- especially smokers and former smokers -- should insist on having a chest X-ray even if they are told they don’t need one, she says.

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Hormones and Lung Cancer

It is also increasingly clear that lung cancer risk differs among male and female nonsmokers.

The recent lung cancer death of actress Dana Reeve, who did not smoke, helped make the public aware that nonsmokers do get lung cancer, Schiller says.

She adds that women with no history of smoking have a greater risk of getting the disease than nonsmoking men, and they tend to be diagnosed at younger ages.

One theory is that just as in breast cancer, the female sex hormone estrogen plays a role in lung cancer.

“It turns out lung cancers, just like breast cancers, have estrogen receptors,” Schiller says. “There is a lot of research looking into whether estrogen can somehow act as a growth-promoting factor in lung cancer, as it does in breast cancer.”

Schiller notes that some recent studies have found that women with lung cancer who take estrogen hormone therapy have a worse cancer survival rate than women who do not take estrogen.

Whatever the cause of the gender differences, Henschke and Schiller agree that increasing awareness about lung cancer risk among women is critical.

More than 73,000 women in the U.S. are expected to die of the disease this year, according to the American Cancer Society.

“Lung cancer kills more women each year than breast, ovarian, and uterine cancer combined,” Schiller says. “If we expect to change this we have to bring this disease into the open and make sure women know they are at risk.”

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By Salynn Boyles, reviewed by Louise Chang, MD

SOURCES: Henschke, C.I. The Journal of the American Medical Association, July 12, 2006; vol 296: pp 180-184. Claudia Henschke, PhD, MD, professor of radiology, Joan and Sanford I. Weill Medical College, Cornell University, New York, City. Joan Schiller, MD, president, National Lung Cancer Partnership; chairwoman, Hematology/Oncology, University of Texas Southwestern Medical Center.