A Pooled Analysis on the Associations between Involuntary Smoking and Lung Cancer Risk by Histological Types

Background: While the association between involuntary tobacco smoke exposure and lung cancer is well established, few studies with sufficient power have been conducted to evaluate the relationship between involuntary smoking (IS) and lung cancer by histological type, especially for the association between IS and small cell lung cancer among nonsmokers. Methods: We evaluated the associations between IS and lung cancer by histological type based on a pooled data of the International Lung Cancer Consortium (ILCCO). The individual-level epidemiological data from 17 participating studies were pooled, including 2,218 non-smoking lung cancer cases and 6,243 non-smoking controls. Logistic regression models were used to obtain adjusted odds ratios (OR) and 95% confidence intervals (CI), using SAS v9. Likelihood ratio tests were used to assess heterogeneity by study site. Results: Among never tobacco smokers, IS exposure was associated with lung cancer with an adjusted OR of 1.33 (95% CI 1.18, 1.50), compared to never exposure to IS, when adjusting for age, sex, ethnicity, and study site. Similar associations were observed in different histological types of lung cancer with adjusted ORs of 1.38 (95% CI 0.97, 1.98) for squamous cell carcinoma, 1.26 (95% CI 1.08, 1.46) for adenocarcinoma, 2.92 (95% CI 1.55, 5.48) for small cell lung cancer, and 1.30 (95% CI 1.14, 1.49) for non-small cell lung cancer. Similar associations with ever IS exposure were observed when the overall population including nonsmokers and smokers was included in the analysis. No apparent association was observed with IS exposure in childhood. Conclusion: This is the first study with a relatively large sample size investigating the relationship between IS exposure and small cell lung cancer among nonsmokers. Our results corroborated the association between IS and lung cancer regardless of histological types, including adenocarcinoma, and we observed the strongest association between IS and small cell lung cancer. Our study provides more precise estimates of the impact of IS on major histological types of lung cancer and suggests the importance of smoking intervention for lung cancer prevention, especially for small cell lung cancer type. This abstract is one of the 17 highest scoring abstracts of those submitted for presentation at the 34th Annual Meeting of the American Society of Preventive Oncology, to be held March 20-23, 2010 in Bethesda, MD.