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Updated population-based data showed that while lung cancer incidence rates are continuing to decline in the U.S., the higher rates previously observed in women versus men have not only persisted in those younger than 50, but now extend to women ages 50 to 54.

As measured in 5-year increments, the overall decline in incidence rates between 2000-2004 and 2015-2019 was of greater magnitude in young men, leading to a higher incidence in women ages 35 to 54, reported Ahmedin Jemal, DVM, PhD, of the American Cancer Society, and colleagues.

Among individuals ages 50 to 54, the rate per 100,000 person-years decreased by 44% in men (from 65.6 to 36.8) and by 20% (48.1 to 38.5) in women, they noted in a research letter published in .

Accordingly, the female to male incidence rate ratio for that age group increased from 0.73 (95% CI 0.72-0.75) during 2000-2004 to 1.05 (95% CI 1.02-1.08) during 2015-2019.

This finding confirmed a pattern observed in a from Jemal and colleagues, showing a higher incidence of lung cancer among women in age groups ranging from 30 to 49 from 1995 to 2014.

In the current study, women ages 55 and older continued to have lower incidence rates than their male counterparts, although differences have become increasingly smaller.

For example, Jemal and colleagues found that among persons ages 70 to 74, the female to male incidence rate ratio increased from 0.62 (95% CI 0.61-0.63) during 2000-2004 to 0.81 (95% CI 0.80-0.82) during 2015-2019.

Why are we seeing this shift in the incidence of lung cancer?

"We don't know why," Jemal told 名媛直播. "We know that 80-85% of lung cancer cases occur among ever smokers, current smokers, or former smokers. But, we know that smoking prevalence or intensity of smoking is not higher in women than in men."

Jemal and colleagues also noted that findings from cohort studies do not support of cigarette smoking in women than in men, and that overdiagnosis is unlikely to account for the excess risk in younger women. However, it is possible that substantial reductions in occupational exposures, such as asbestos, could partly explain some of the shift in disease burden between men and women.

Jemal said one hypothesis is that "the reduction in lung cancer risk after smoking cessation varies by the types of lung cancer." For example, he pointed out that the risk of adenocarcinoma, a lung cancer subtype that is more common among women than men, decreases more slowly than the risk of other types of lung cancer after smoking cessation.

"And women have been slower in quitting smoking in large numbers than men," he added, which suggests that smoking cessation efforts should be intensified among young and middle-age women.

"We need more research to understand why lung cancer incidence is higher among these younger women than in men," Jemal said. "It is important to understand this, so that we can better plan interventions."

For this cross-sectional study, the researchers analyzed population-based incidence data on lung and bronchus cancers diagnosed from 2000 to 2019 from the National Cancer Institute's SEER program, covering nearly 50% of the U.S. population. Cases were categorized by sex and age in 5-year increments and year of diagnosis.

The authors acknowledged several limitations to their study, including the lack of individual risk factor data in the database. They also pointed out that while the study did not account for the growth in populations born outside the U.S. during the study period, cigarette smoking is substantially lower in non-U.S.-born women versus men.

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