By Amy Norton
WEDNESDAY, May 23, 2018 (HealthDay News) -- In a reversal of historical patterns, lung cancer is now more common among young U.S. women than men, a new study finds.
The good news, researchers found, is that over the past two decades, lung cancer rates among 35- to 54-year-old Americans have dropped across the board. But the decline has been steeper among men so that now, incidence of the disease is higher in white and Hispanic women born since the mid-1960s.
Among blacks and Asian-Americans, meanwhile, women have caught up with men, according to findings published in the May 24 issue of the New England Journal of Medicine.
The question now is why, said lead researcher Dr. Ahmedin Jemal of the American Cancer Society.
"The higher incidence among women is not fully explained by smoking," he said.
It's true, Jemal said, that American women and men have become increasingly similar in their smoking rates. But men still typically smoke more cigarettes per day. And among Hispanic Americans, he said, smoking remains more common among men than women.
Jemal could only guess about why the lung cancer rate has fallen to a greater degree among men. One possibility, he said, is that female smokers who quit have a slower decrease in their lung cancer risk compared male smokers.
He noted that women and men tend to differ in the types of lung cancer they develop. A form called adenocarcinoma is more common in women -- and the risk of that lung cancer typically dips at a slower rate among former smokers, compared with other forms of the disease.
Some research has suggested women might be more biologically vulnerable to the damaging effects of cigarette smoke. But so far, Jemal said, studies have come to mixed conclusions.
Regardless of the explanation, he said, the message for smokers is clear: Quit as soon as you can.
"Smokers should know that those who quit -- especially by age 40 -- can largely avoid lung cancer," Jemal said.
And while this study focused on younger adults, he added, it's never too late to quit smoking. Even people who kick the habit at relatively older ages can lower their disease risks and add years to their life expectancy.
The findings are based on cases of invasive lung cancer diagnosed in Americans ages 30 to 54 between 1995 and 2014.
In general, the study found, the incidence of the disease dipped over time. But men saw a sharper decrease, so that the traditional male-female pattern flipped.
For example, among Americans born in the mid-1960s, the annual rate of lung cancer at the ages of 45 to 49 was about 25 cases for every 100,000 women. That compared with 23 cases for every 100,000 men.
The pattern was a turnaround from what was seen among Americans born around 1950. In that group, the rate of lung cancer among men in their late 40s was about one-quarter higher, compared with women.
"We don't know why this change has taken place," said Dr. Norman Edelman, senior scientific adviser for the American Lung Association, which was not involved in the study.
But it will be important to figure it out, according to Edelman. "Anything you can learn about lung cancer could eventually help us better treat or prevent the disease," he said.
For smokers -- or kids who are tempted to start -- Edelman said this study highlights a crucial point: Lung cancer can arise at a young age.
"Sometimes young people are immune to messages about long-term health risks that will happen in their 60s," he said. "If they know this can happen at age 40, that could be a very powerful message."
Edelman also stressed that many smokers need five or more tries before they successfully quit. But, he said, help is out there, and smokers should keep trying until they find that tactic that works.
In general, Edelman said, a combination of medication and some form of support program is most effective.