The data from the EPIC study were drawn from a case–control lung cancer study nested within the EPIC cohort. Blood and questionnaire data on self-reported smoking behavior were collected in a prospective manner as part of the recruitment procedure and before cancer diagnosis in case subjects (41). However, cotinine levels and self-reported cigarette consumption in current smokers differed between case subjects (EPIC Case) and control subjects (EPIC Control). Mean cotinine levels were higher in the EPIC Case subsample (1391 nmol/L, SD = 588 nmol/L) than the EPIC Control subsample (1006 nmol/L, SD = 589 nmol/L) even after adjustment for cigarette consumption (two-sided Kruskal–Wallis P < .001), indicating possible differences in smoking behavior (eg, depth of inhalation). This difference at baseline may have contributed to the likelihood of a subsequent lung cancer diagnosis. Therefore, the EPIC case subjects and control subjects were analyzed and presented separately in this study.
