The incidence of lung cancer appears to be higher among young women compared with young men in the United States as well as 5 other countries. Historically, the incidence of lung cancer has been higher among men than women because a larger population of men began smoking sooner (and smoke more often) than women. The findings were recently published in International Journal of Cancer.

To identify lung and bronchial cancer cases, the study researchers used national or subnational registry data that were accepted for publication in Cancer Incidence in Five Continents volumes VIII to XI. These data were used to calculate 5-year age-specific lung cancer incidence rates for men and women, and the incidence rates were grouped by estimated birth year and histologic subtype.

Overall, 6 countries — Canada, Denmark, Germany, New Zealand, the Netherlands, and the United States — had a chronological shift from lung cancer incidence rates being higher among young men to rates being higher among young women. For example, the female-to-male incidence rate ratio shifted from 0.7 (95% CI, 0.6–0.8) to 1.5 (95% CI, 1.4–1.7) among women in the Netherlands aged 45 to 49 years. In the United States, lung cancer incidence rates for women were higher among those aged 40 to 44 years and 45 to 49 years.

The higher lung cancer incidence rates among young women could not be explained by a difference in smoking, as the prevalence of smoking among women was never higher than that for men across the 6 countries.

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Known contributors to lung cancer, including type of tobacco use, intensity and duration of smoking, and age at which smoking began, were unknown for the 6 countries and therefore, could not be evaluated.

According to the study researchers, an earlier study in the United States indicated that type of tobacco use and intensity of smoking were “unlikely” to explain why young women had a higher incidence of lung cancer incidence.

“As our results cannot be fully explained by tobacco use, other risk factors for lung cancer, nor screening, it is possible that females may be at an increased risk of lung cancer compared to males,” the study researchers wrote.

Reference

Fidler-Benaoudia MM, Torre LA, Bray F, Ferlay J, and Jemal A. Lung cancer incidence in young women vs. young men: A systematic analysis in 40 countries [published online February 5, 2020]. Int J Cancer. doi: 10.1002/ijc.32809.

This article originally appeared on Cancer Therapy Advisor