alexa Lung Cancer Death Rates in Lifelong Nonsmokers
Pulmonology

Pulmonology

Journal of Clinical Respiratory Diseases and Care

Author(s): Thun MJ

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Background:

Few studies have directly measured the age-, sex-, and race-specific risks of lung cancer incidence and mortality among never tobacco smokers. Such data are needed to quantify the risks associated with smoking and to understand racial and sex disparities and temporal trends that are due to factors other than active smoking. Methods: We measured age-, sex-, and race-specific rates (per 100 000 person-years at risk) of death from lung cancer among more than 940 000 adults who reported no history of smoking at enrollment in either of two large American Cancer Society Cancer Prevention Study cohorts during 1959–1972 (CPS-I) and 1982–2000 (CPS-II). We compared lung cancer death rates between men and women and between African Americans and whites and analyzed temporal trends in lung cancer death rates among never smokers across the two studies by using directly age-standardized rates as well as Poisson and Cox proportional hazards regression analyses. All statistical tests were two-sided. Results: The age-standardized lung cancer death rates among never-smoking men and women in CPS-II were 17.1 and 14.7 per 100 000 person-years, respectively. Men who had never smoked had higher age-standardized lung cancer death rates than women in both studies (CPS-I: hazard ratio [HR] = 1.52, 95% confidence interval [CI] = 1.28 to 1.79; CPS-II: HR = 1.21, 95% CI = 1.09 to 1.36). The rate was higher among African American women than white women in CPS-II (HR = 1.43, CI = 1.11 to 1.85). A small temporal increase (CPS-II versus CPS-I) in lung cancer mortality was seen for white women (HR = 1.25, CI = 1.12 to 1.41) and African American women (HR = 1.22, CI = 0.64 to 2.33), but not for white men (HR = 0.89, CI = 0.74 to 1.08). Among white and African American women combined, the temporal increase was statistically significant only among those aged 70–84 years (P<.001). Conclusions: Contrary to clinical perception, the lung cancer death rate is not higher in female than in male never smokers and shows little evidence of having increased over time in the absence of smoking. Factors that affect the interpretation of lung cancer trends are discussed. Our novel finding that lung cancer mortality is higher among African American than white women never smokers should be confirmed in other studies. Approximately 85%–90% of all lung cancer deaths in the United States are caused by active cigarette smoking (1). The remaining 10%–15% represent between 17 000 and 26 000 deaths annually (2), a number that would rank among the six to eight most common fatal cancers in the United States if considered as a separate category (3,4). An estimated 15 000 lung cancer deaths caused by factors other than active cigarette smoking occur in lifelong non-smokers; the rest are combined with and statistically indistinguishable from the much larger number caused by cigarette smoking among current and former smokers. Known causes of lung cancer other than cigarette smoking include secondhand smoke, active smoking of other tobacco products, and exposure to other carcinogens such as asbestos, radon, radiation therapy, combustion products, and various other exposures in occupational, environmental, and/or medical settings. Information on lung cancer risk among lifelong nonsmokers is needed to understand racial and sex disparities in incidence and mortality, to determine whether lung cancer occurrence has changed over time because of factors other than active smoking, and to quantify the risks associated with smoking. Such information also helps to inform ongoing scientific debates, such as whether women are more susceptible to lung cancer than men in the presence (5–7) or absence (5,8) of current cigarette smoking and whether factors other than active smoking contribute to the disparity in lung cancer risk between African Americans and whites (9–11). Despite the need for these data, it is surprisingly difficult to obtain reliable and precise measurements of lung cancer risk among lifelong nonsmokers. Smoking histories are not collected routinely by population-based cancer registries or on death certificates; smoking information that is available from next of kin or hospital records is incomplete and often unreliable. Studies published in the early 1960s estimated age- and sex-specific lung cancer death rates in never smokers from a 10% sample of U.S. deaths in 1958 and 1959 and from interviews of selected households (12,13). However, the age categories were broad, the smoking information was collected from next of kin, and the number of never smokers was estimated indirectly. Three large cohort studies have reported age-specific death rates from lung cancer in never-smoking men and women (14–17), but did not present data separately for African Americans, and in some reports (18–20) combined the results for occasional and never smokers. Analyses from the Multiethnic Cohort (21) demonstrate that most of the difference in lung cancer risk between African Americans and whites is attributable to different smoking practices, but there were too few cancers among never-smokers in this cohort to measure race-, sex-, and age-specific incidence rates precisely in persons who never smoked. Smaller cohort studies and all case–control studies typically report only the relative risk of lung cancer in smokers compared with that in never smokers. In this study we examined age-, sex-, and race-specific death rates from lung cancer among more than 940 000 white and African American adults who reported no history of tobacco use when enrolled in either of two large American Cancer Society (ACS) studies. The Cancer Prevention Study I (CPS-I) began in the fall of 1959 and ended follow-up in July 30, 1972. The Cancer Prevention Study II (CPS-II) began in the fall of 1982 and has ongoing follow-up of mortality. The analyses of CPS-II in our paper are based on 20 years of follow-up, increasing the number of lung cancer deaths among never smokers from less than 440 in previous reports (15,16,22) to 1498 here. The massive size and similar methods of enrollment and follow-up of these cohorts provide a unique longitudinal perspective on changes in lung cancer mortality in relation to smoking over the last 50 years.

This article was published in Journal of the National Cancer Institute and referenced in Journal of Clinical Respiratory Diseases and Care

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