Estimating lung cancer risk with exposure to environmental tobacco smoke.

Estimates of lung cancer in nonsmokers due to exposure to environmental tobacco smoke (ETS) in the workplace or in the home may be developed in several ways. Estimates may be based on (italic)a(/italic)) models developed using the full range of data in smokers; (italic)b(/italic)) models developed using data restricted to smokers with a low smoking rate, for example, (3/4) 10 cigarettes per day; (italic)c(/italic)) models developed using data from studies of residential exposure to ETS of nonsmokers, with exposures based on smoking rates of spouses; and (italic)d(/italic)) models using data from studies of occupational exposure to ETS of nonsmokers. Methods (italic)a(/italic) and (italic)b(/italic) require an estimate of cigarette equivalent exposure for ETS as well as assumptions on the cigarette equivalent dose to target cells from ETS and on the comparability of lung cancer risk per unit dose from smokers and nonsmokers. Summary relative risks (RRs) and 95% confidence intervals (CI) from ETS studies of nonsmokers with exposures based on smoking patterns of spouses are 1.24 (1.1, 1.4) for females and 1.34 (1.0, 1.8) for males, whereas the RR estimate for occupational ETS exposure and its 95% CI is 1.39 (1.2, 1.7). Using RR estimates for ETS exposure, cigarette equivalents for ETS range from 0.1 to 1.0, based on a range of descriptive and biologically motivated models in active smokers; a cigarette equivalent is 0.2 based on a comparison of log-linear trends in RR with number of cigarettes smoked per day in active smokers and in spouses of nonsmokers.