Lung cancer mortality in relation to age, duration of smoking, and daily cigarette consumption: results from Cancer Prevention Study II.

The magnitude of the effect of smoking duration on lung cancer mortality relative to that of intensity (cigarettes/day) has practical implications for both tobacco control policy and research. This issue was addressed by R. Doll and R. Peto (J. Epidemiol. Commun. Health, 32: 303-313, 1978) in their historic analysis of one of the few large cohort studies in which intensity and duration were estimated separately. Their findings have been interpreted to mean that smoking duration is much more important than smoking intensity in causing lung cancer. The separate contributions of smoking duration and intensity to lung cancer risk have not been evaluated in other large prospective studies. We studied participants in the Cancer Prevention Study II, followed from 1982 through 1988. After restricting to people 40-79 years old who smoked < or =40 cigarettes per day at enrollment, we fit Poisson models for four age groups and evaluated lung cancer mortality (M) in relation to smoking duration (D) and intensity (I) on a double-log scale, as suggested by the Armitage-Doll multistage carcinogenesis model. The age-specific mortality estimates for men (M(m)) and for women (M(w)), when transformed to the original scale, were: ages 40-49: M(m) = e(-17.9) x D(1.9) x I(0.95), M(w) = e(-20.2) x D(2.8) x I(0.96); ages 50-59: M(m) = e(-17.4) x D(2.6) x I(0.52), M(m) = e(-17.2) x D(2.2) x I(0.75); ages 60-69: M(m) = e(-15.7) x D(2.4) x I(0.37), M(m) = e(-14.1) x D(1.5) x I(0.78); ages 70-79: M(m) = e(-13.0) x D(1.8) x I(0.39), M(m) = e(-13.2) x D(1.3) x I(0.95). Our study confirms that years of cigarette smoking is far more important than the number of cigarettes smoked per day in predicting lung cancer risk in United States men, regardless of age, and provides new evidence that a qualitatively similar pattern holds for women. The results support measures to prevent the uptake of smoking by adolescents and increase cessation. We discuss reasons why the associations we observe are lower than those reported by R. Doll and R. Peto (J. Epidemiol. Commun. Health, 32: 303-313, 1978).