Date Published: September 9, 2008
Publisher: Public Library of Science
Author(s): Michael J Thun, Lindsay M Hannan, Lucile L Adams-Campbell, Paolo Boffetta, Julie E Buring, Diane Feskanich, W. Dana Flanders, Sun Ha Jee, Kota Katanoda, Laurence N Kolonel, I-Min Lee, Tomomi Marugame, Julie R Palmer, Elio Riboli, Tomotaka Sobue, Erika Avila-Tang, Lynne R Wilkens, Jon M Samet, Hans-Olov Adami
Abstract: BackgroundBetter information on lung cancer occurrence in lifelong nonsmokers is needed to understand gender and racial disparities and to examine how factors other than active smoking influence risk in different time periods and geographic regions.Methods and FindingsWe pooled information on lung cancer incidence and/or death rates among self-reported never-smokers from 13 large cohort studies, representing over 630,000 and 1.8 million persons for incidence and mortality, respectively. We also abstracted population-based data for women from 22 cancer registries and ten countries in time periods and geographic regions where few women smoked. Our main findings were: (1) Men had higher death rates from lung cancer than women in all age and racial groups studied; (2) male and female incidence rates were similar when standardized across all ages 40+ y, albeit with some variation by age; (3) African Americans and Asians living in Korea and Japan (but not in the US) had higher death rates from lung cancer than individuals of European descent; (4) no temporal trends were seen when comparing incidence and death rates among US women age 40–69 y during the 1930s to contemporary populations where few women smoke, or in temporal comparisons of never-smokers in two large American Cancer Society cohorts from 1959 to 2004; and (5) lung cancer incidence rates were higher and more variable among women in East Asia than in other geographic areas with low female smoking.ConclusionsThese comprehensive analyses support claims that the death rate from lung cancer among never-smokers is higher in men than in women, and in African Americans and Asians residing in Asia than in individuals of European descent, but contradict assertions that risk is increasing or that women have a higher incidence rate than men. Further research is needed on the high and variable lung cancer rates among women in Pacific Rim countries.
Partial Text: Most of the more than 1.4 million lung cancer deaths that occur annually worldwide are caused by tobacco smoking . The rest comprise only a small fraction of the total, yet they account for a substantial disease burden. For example, in the United States (US), factors other than cigarette smoking are estimated to account for 10%–15% of all lung cancer deaths  on the basis of surveys of smoking in the general population and relative risk estimates from a large American Cancer Society cohort study . This percent range corresponds to between 16,000 and 24,000 of the more than 161,000 lung cancer deaths projected to occur in the US in 2008 . If these deaths were considered as a separate category, they would rank among the seven to nine most common fatal cancers in the US .
To our knowledge, this is the first comprehensive effort to pool and compare data on lung cancer incidence and death rates in lifelong nonsmokers from multiple sources. The combination of data from cohort studies and population registries provides a more coherent picture of how background lung cancer risk varies by age, sex, geographic location, race/ethnicity, and time period than can be obtained from any single study. All of the available data have limitations and unknowns regarding the accuracy of the diagnostic information, the validity and comparability of the exposure information on active smoking or its absence, and the lack of measurements of other exposures that affect lung cancer risk. In the interest of clarity, however, we first discuss the series of questions raised in the introduction and later consider how these data limitations could affect our conclusions.