There is a recent trend of more lung cancer cases in adult women compared to men, unrelated to smoking, a new study has found.

The “emerging pattern of higher lung cancer incidence in young females” is not confined to geographic areas and incomes levels and “is not fully explained by sex-differences in smoking prevalence,” the authors comment.

Miranda M. Fidler-Benaoudia, PhD, Cancer Control Alberta, Alberta Health Services, Calgary, Canada, and colleagues examined lung cancer cases in 40 countries from 1993 to 2012.

They found that the female-to-male incidence rate ratio (IRR) had significantly crossed over from men to women in six countries, including the United States and Canada, and had nonsignificantly crossed over in a further 23 countries. The research was published online February 5 in the International Journal of Cancer.