Attributable risk of lung cancer in lifetime nonsmokers and long-term ex-smokers (Missouri, United States)

A population-based, case-control study of incident lung cancer among women in Missouri (United States) who were lifetime nonsmokers and long-term ex-smokers was conducted between 1986 and 1992. The study included 618 lung cancer cases and 1,402 population-based, age matched controls. Information on lung-cancer risk factors was obtained by interviewing cases, next-of-kin of cases (36 percent and 64 percent of the cases, respectively) and controls. Year-long radon measurements also were sought in every dwelling occupied for the previous five to 30 years. Population attributable risks (PAR) for specific risk factors were computed for all subjects, for lifetime nonsmokers, for long-term ex-smokers, by histologic cell type (i.e., adenocarcinoma cf nonadenocarcinoma) and for direct interviews with case (for living cases) and for next-of-kin interviews (for dead cases or cases too ill to complete an interview). The mean age at lung cancer diagnosis was 71 years, and nearly 50 percent of the lung cancers were histologically confirmed adenocarcinomas. Almost 40 percent of all lung cancers among lifetime nonsmokers and almost 50 percent of lung cancers among all subjects could be explained by the risk factors under study. Dietary intake of saturated fat and nonmalignant lung disease were the two leading identified risk factors for lung cancer among the lifetime nonsmokers, followed by environmental tobacco smoke, and occupational exposures to known carcinogens. A small nonsignificant risk was found for study subjects exposed to median domestic radon concentration of 4 pCi/l (25-year time-weight average). Since only a small fraction of the population is exposed at this level, it is estimated that the PAR for domestic radon was less than two percent in Missouri. The risk for saturated fat intake was similar for lifetime nonsmokers, ex-somkers, adenocarcinoma cases, and nonadenocarcinoma cases; however, the increased risk was much more pronounced for next-of-kin interviews (PAR=31 percent) than for interviews with the study subjects (PAR = nine percent). A similar pattern of PAR was identified among ex-smokers but, in this group, the lingering effect of a history of smoking was also very important. Along with saturated fat intake (PAR=20 percent), the combined effect of previous active and passive smoking even after 15 years of cessation of active smoking was responsible for more lung cancer than any other risk factor under study (PAR=59 percent).