Kelly Journalist, with her daughter Emma Jane, was diagnosed with lung cancer at 32. (Courtesy of Kelly Journalist)

Reversing a historic trend, rates of lung cancer among younger white and Hispanic women have surpassed those of men — and the change cannot be fully explained by gender differences in smoking behavior, researchers said Wednesday.

Previous research pointed to shifts in the incidence of lung cancer, with rates creeping up among some groups of women. The new study, published in the New England Journal of Medicine, is the largest and most definitive on the topic and one that incorporates smoking patterns and tumor characteristics in its analysis, according to its authors.

The research, a collaboration of the American Cancer Society and the National Cancer Institute, doesn't explain why lung-cancer rates for white and Hispanic women born since the mid-1960s are higher than for men. But it raises some possibilities, including biological and genetic ones, that other scientists are pursuing.

It notes, for example, that when people stop smoking their risk of developing cancer drops every year. But the risk for adenocarcinoma, a common type of the disease, drops more slowly than that for other types of lung cancer. And women are more likely then men to develop adenocarcinoma.

“One hypothesis is that the reduction in the risk of lung cancer after smoking cessation may be slower in women than in men,” said cancer society epidemiologist Ahmedin Jemal, who led the study.  

The researchers analyzed all cases of invasive lung cancer in people ages 30 to 54 from 1995 through 2014 in most of the United States.

Overall, they found lung cancer rates have fallen for both men and women in that group over the past two decades, but the drops have been steeper for men. As a result, the historic pattern of higher lung cancer rates among men has flipped, with the rates now higher for the white and Hispanic women. (Among those ages, black women's rates remain below those of black men.)

That finding confirms what many doctors say: They are seeing more female lung cancer patients than in the past.

“Lung cancer doctors are all having this experience of seeing more and more women patients and more and more patients who have never smoked,” said Marc Ladanyi, a lung cancer researcher and chief of molecular diagnostics at Memorial Sloan Kettering Cancer Center, who wasn't involved in the study.

Ladanyi led a 2012 study that suggested female smokers are more likely than men to develop a specific genetic mutation that is implicated in adenocarcinoma.

In the study published Wednesday, the incidence rate for lung cancer remains higher in men than women when all races and ages are combined. It was only when researchers looked at specific age and race subgroups that new patterns emerged.

For example, while smoking prevalence among Hispanic women is much less than among their male counterparts, their lung cancer rate is higher.

Bryan Stanifer, a thoracic surgeon and director of the Women’s Lung and Health Center at NewYork-Presbyterian Columbia University Medical Center, suspects that some women have “a genetic predisposition” that makes them more susceptible to lung cancer, especially when combined with some sort of environmental toxin such as secondhand smoke. What's puzzling, he said, is that many of his patients haven't been around smoke.

That was the case with Kelly Journalist, 35, who three years ago developed a persistent cough. She tried taking antibiotics, buying an air purifier and kicking her 75-pound Golden Retriever off her bed. After an X-ray and other tests revealed a mass on her right lung, she had surgery at NewYork-Presbyterian.

When the pathology report came back showing cancer, “it was a shock,” she said. “I have never been a smoker or been in an environment of smokers, and I was only 32.” Because her malignancy was caught at a very early stage, she didn't have to get chemotherapy or radiation and has not had a recurrence.

Lung cancer is the leading cancer killer in the United States and the world. The American Cancer Society estimates that more than 234,000 people will be diagnosed in the United States this year, and about 154,000 will die of the disease. About 85 percent of cases are due to smoking, experts say.

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