Objective: To determine the relative risk (RR) of lung cancer in lifetime never smokers associated with environmental tobacco smoke (ETS) exposure.
Design: Multicenter population-based case-control study.
Setting: Five metropolitan areas in the United States: Atlanta, Ga, Houston, Tex, Los Angeles, Calif, New Orleans, La, and the San Francisco Bay Area, Calif.
Patients or other participants: Female lifetime never smokers: 653 cases with histologically confirmed lung cancer and 1253 controls selected by random digit dialing and random sampling from the Health Care Financing Administration files for women aged 65 years and older.
Main outcome measure: The RR of lung cancer, estimated by adjusted odds ratio (OR) with 95% confidence interval (CI), associated with ETS exposure.
Results: Tobacco use by spouse(s) was associated with a 30% excess risk of lung cancer: all types of primary lung carcinoma (adjusted OR = 1.29; P < .05), pulmonary adenocarcinoma (adjusted OR = 1.28; P < .05), and other primary carcinomas of the lung (adjusted OR = 1.37; P = .18). An increasing RR of lung cancer was observed with increasing pack-years of spousal ETS exposure (trend P = .03), such that an 80% excess risk of lung cancer was observed for subjects with 80 or more pack-years of exposure from a spouse (adjusted OR = 1.79; 95% CI = 0.99 to 3.25). The excess risk of lung cancer among women ever exposed to ETS during adult life in the household was 24%; in the workplace, 39%; and in social settings, 50%. When these sources were considered jointly, an increasing risk of lung cancer with increasing duration of exposure was observed (trend P = .001). At the highest level of exposure, there was a 75% increased risk. No significant association was found between exposure during childhood to household ETS exposure from mother, father, or other household members; however, women who were exposed during childhood had higher RRs associated with adult-life ETS exposures than women with no childhood exposure. At the highest level of adult smoke-years of exposure, the ORs for women with and without childhood exposures were 3.25 (95% CI, 2.42 to 7.46) and 1.77 (95% CI, 0.98 to 3.19), respectively.
Conclusion: Exposure to ETS during adult life increases risk of lung cancer in lifetime nonsmokers.