Lung Cancer Rates Among Women Are Falling Much Slower Than Those in Men. Here's WhyLung cancer is the deadliest form of cancer in the U.S. But mortality rates have been falling for decades, driven by medical advances and historic decreases in cigarette smoking. The benefits, however, have not been shared equally. What was historically a men’s disease is now disproportionately affecting women. A 2018 study in the New England Journal of Medicine showed that rates of lung-cancer incidence actually rose over the past 20 years among women born around either 1950 or 1960; in younger women, diagnoses fell, but not as much as among men.

Perhaps more puzzling, Dr. Ahmedin Jemal, co-author of the study, says smoking habits cannot totally explain the demographic shift in lung cancer. But for a few historical blips, U.S. smoking rates have been higher among men than women, continuing to the present day, Jemal says. As of 2017, almost 16% of adult men smoked, compared with about 12% of women, according to federal data. What’s more, though nonsmokers account for about 15% of all lung-cancer diagnoses, 24% of the U.S. women diagnosed in 2016 were nonsmokers like Hollenbeck. That means other factors are contributing to the troubling trend. “It’s completely unknown right now,” says Alice Berger, who researches genetics and cancer at Seattle’s Fred Hutchinson Cancer Research Center.

Scientists are beginning to zero in on some clues. Research shows that the type of lung cancer most common among nonsmokers disproportionately affects women, and young women are more likely to have a gene mutation often found in the tumors of nonsmokers. (A silver lining, Berger says, is that the mutation responds well to newer targeted cancer therapies.) Quirks of female sex hormones or women’s immune systems could be responsible, Berger says. But research is ongoing, so for now those ideas remain theories.

Other hypotheses focus on how cigarettes affect women who do smoke. Jemal says something about female biology could make women more susceptible than men to genetic mutations caused by carcinogens in cigarettes. If so, a higher percentage of women who pick up the habit could develop cancer, relative to men. But that, too, remains a theory requiring deeper investigation.

Without firm answers about the risks women face, doctors, patients and advocates are spreading the word about lung cancer among women and nonsmokers. About 1,400 people have joined a Facebook support group. Our society believes that lung cancer is a smoking disease. But for young women, that’s increasingly untrue.

The information in this article was written by Jamie Ducharme and originally published in Time Magazine.