Lung cancer occurrence in never-smokers: an analysis of 13 cohorts and 22 cancer registry studies

Abstract

Background: Better 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 findings: We 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.

Conclusions: These 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.

Figure 1. Age-Specific Lung Cancer Mortality Rates Comparing Current Smokers with Never-Smokers in Two Large Cohorts

Blue line indicates never-smokers; red line indicates current smokers.

Figure 2. Sex- and Age-Specific Lung Cancer Death Rates in Three Large Cohorts

(A–C) Blue line indicates men; red line indicates women.

Figure 3. Age-Standardized Lung Cancer Death Rates by Race and Sex in the Pooled Analyses

Figure 4. Sex- and Age-Specific Lung Cancer Incidence Rates in Individuals of European Descent, with and without CPS-II Nutrition Cohort

(A–C) Blue line indicates men; red line indicates women.