Active and passive smoking in relation to lung cancer incidence in the Women's Health Initiative Observational Study prospective cohort

Abstract

Background: Lung cancer is the leading cause of worldwide cancer deaths. While smoking is its leading risk factor, few prospective cohort studies have reported on the association of lung cancer with both active and passive smoking. This study aimed to determine the relationship between lung cancer incidence with both active and passive smoking (childhood, adult at home, and at work).

Patients and methods: The Women's Health Initiative Observational Study (WHI-OS) was a prospective cohort study conducted at 40 US centers that enrolled postmenopausal women from 1993 to 1999. Among 93 676 multiethnic participants aged 50-79, 76 304 women with complete smoking and covariate data comprised the analytic cohort. Lung cancer incidence was calculated by Cox proportional hazards models, stratified by smoking status.

Results: Over 10.5 mean follow-up years, 901 lung cancer cases were identified. Compared with never smokers (NS), lung cancer incidence was much higher in current [hazard ratio (HR) 13.44, 95% confidence interval (CI) 10.80-16.75] and former smokers (FS; HR 4.20, 95% CI 3.48-5.08) in a dose-dependent manner. Current and FS had significantly increased risk for all lung cancer subtypes, particularly small-cell and squamous cell carcinoma. Among NS, any passive smoking exposure did not significantly increase lung cancer risk (HR 0.88, 95% CI 0.52-1.49). However, risk tended to be increased in NS with adult home passive smoking exposure ≥30 years, compared with NS with no adult home exposure (HR 1.61, 95% CI 1.00-2.58).

Conclusions: In this prospective cohort of postmenopausal women, active smoking significantly increased risk of all lung cancer subtypes; current smokers had significantly increased risk compared with FS. Among NS, prolonged passive adult home exposure tended to increase lung cancer risk. These data support continued need for smoking prevention and cessation interventions, passive smoking research, and further study of lung cancer risk factors in addition to smoking. CLINICALTRIALS.GOV: NCT00000611.

Keywords: lung cancer; lung cancer histology; never smokers; passive smokers; smoking.

© The Author 2014. Published by Oxford University Press on behalf of the European Society for Medical Oncology. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Figures

Figure 1.

Event-free survival estimates with (A) number of subjects at risk, stratified by smoking status; and (B) number of subjects at risk, with further stratification of never smokers (passive/no passive exposure). Kaplan–Meier event-free survival plots are presented stratified by smoking status (current, former, never–no passive, and never-passive). Log-rank test of equality over smoking categories has P < 0.0001. When never smokers are further segmented, the hazards for never, no passive exposure and never, passive exposure cross over each other at several points and do not seem to be different from each other.