While lung cancer rates have historically been higher among men, new findings published in The New England Journal of Medicine reveal that lung cancer incidence in the United States is now higher among women compared with men, reports the American Cancer Society (ACS).

For the study, the ACS and the National Cancer Institute teamed up to examine lung cancer incidence based on sex, race or ethnic group, age, year of diagnosis and year of birth. Researchers specifically analyzed lung cancer diagnoses among people ages 30 to 54 from 1995 to 2014.

Although the overall incidence of lung cancer declined in both men and women in this age group during the 20-year period, the decline was much steeper among men.

Furthermore, scientists found that there was a reversal in lung cancer incidence between men and women of white and Hispanic origin who were born since the mid-1960s. Lung cancer rates were now much higher among women than men.

Researchers don’t believe smoking behaviors are responsible for this change because men continue to smoke at higher rates than women.

Other possible reasons for this gender crossover, according to the study authors, include the differences in the types of lung cancer that affect men versus women and the reduction in risk associated with these types after quitting smoking.

These findings “may foreshadow a higher future burden of overall lung cancer among women than among men as younger cohorts age, which further underscores the need to intensify anti-tobacco measures to decrease smoking among young women,” conclude researchers.