The smokers used in this study were participants in the American Cancer Society CPS-II Cohort, a prospective study of cancer mortality begun in 1982, and the CPS-II Nutrition Cohort, a prospective study of cancer incidence formed in 1992 using a subset of CPS-II participants. Approximately 1.2 million Americans, who were recruited from all 50 states and had a median age of 57 in 1982, were enrolled in CPS-II. All participants completed a self-administered baseline questionnaire at enrollment which included questions on lifetime history of smoking behavior, demographic, medical, lifestyle, environmental, and dietary characteristics. In 1992, approximately 184,000 CPS-II participants were enrolled in the CPS-II Nutrition Cohort and completed a mailed questionnaire that included questions on smoking behavior, demographics, diet, and other lifestyle factors. The recruitment and characteristics of this cohort have been described elsewhere (14). Follow-up questionnaires were sent to all living Nutrition Cohort members in 1997 and every two years afterwards to update exposure information and to ascertain newly diagnosed cases of cancer. Incident cases reported via questionnaire response were verified through medical records, linkage with state cancer registries, or death certificates (14).
