Lung cancer remains the number one killer for both men and women in the United States, claiming an estimated 160,000 lives this year. The vast majority of cases occur in smokers or former smokers, but around 20,000 non-smokers also succumb to this devastating disease. Recently, some studies have indicated that lung cancer in non-smokers is increasing, and that women are more susceptible to it than men.

However, a new study from an international team of researchers found the opposite: that men have a higher death rate from lung cancer across all age groups and all ethnic groups examined. Scientists combined information from 13 studies and 22 cancer registries in 10 countries in their analysis. They found no evidence that lung cancer rates are on the rise among non-smokers.

Researchers continue to search for causes of lung cancer among this otherwise low risk group - thus far studies implicate asbestos, radon, radiation treatments, and exposure to second-hand tobacco smoke.

ABC's Dr. Timothy Johnson reports: