Sept. 9, 2008 -- Researchers looking into lung cancers in nonsmokers have found that men seem to die from the disease more than women.

The reasons for this are not clear from the study results.

Researchers led by the American Cancer Society's Michael Thun, MD, looked at data to try to better understand how lung cancer affects men and women in different cultures and from different time periods.

They pooled information on lung cancer rates and deaths from 13 large groups representing about 2 million people around the world.

Researchers also abstracted data for women from 22 cancer registries and 10 countries in places where few women smoked.

All the participants were self-described nonsmokers.

Here are the main findings:

Men died more from lung cancer than did women in all age and racial groups studied.

Women and men 40 years old and older had similar rates of lung cancer, when the figures were standardized.

African-Americans -- and Asians living in Korea and Japan -- had higher death rates from lung cancer than did people of European extraction.

There were no time trends seen when researchers compared lung cancer rates and death rates among U.S. women ages 40 to 69 during the 1930s to nonsmoking women of today's population.

Women in East Asia had higher and more variable lung cancer rates than did women in other areas of the world where women don't smoke very much.

According to the American Cancer Society, in the U.S. 10% to 15% of all lung cancer deaths are caused by something other than smoking cigarettes. The organization also finds that nearly 1.5 million people die from lung cancer every year around the world due to tobacco smoking.

In background information published with the study results, researchers write that tumors in the lungs of people who are not smokers have "different molecular profiles and respond better to targeted therapies" than do tumors in smokers' lungs.

Researchers call for more study, noting that these findings contradict with earlier research suggesting that the risk of lung cancer in nonsmoking women and men has increased and that nonsmoking women get lung cancer more than men do.

The findings appear in September's issue of PLoS Medicine.