ORs of lung cancer risk for each pack-year of exposure was shown to increase with increasing intensity of smoking only for subjects who smoke up to 20 cigarettes per day (33). We observed similar results in the current study, where little excess in risk was noted for those reporting above 20 CPD (Figure 1). As expected, we also observed that cases reporting similar tobacco consumption levels had higher cotinine levels than controls, even after accounting for number of cigarettes smoked over the last 24 hours hours (mean cotinine level in controls adjusted for number of cigarettes smoked in last 24 hours = 1113 nmol/L vs mean cotinine level in cases = 1433 nmol/L; P < 0.001). In contrast with CPD, the relationship between cotinine and risk increased monotonically, consistent with previous observations reported by Boffetta et al.(37) Similarly, Yuan et al.(40) observed an association of cotinine with lung cancer risk among smokers with comparable smoking history, but no association was detected by Church et al.(41) in current smokers. In mutually adjusted analysis of cotinine and CPD, the association of cotinine with risk was considerably less attenuated than that of CPD. This is consistent with the notion that circulating cotinine captures
