Prospective study of cigarette smoking and adult glioma: dosage, duration, and latency.

Tobacco products are major contributors of exogenous N-nitroso compounds, a group of potent neurocarcinogens. Overall results from studies of smoking and brain tumors have been null, but have provided little information on duration, age at smoking initiation, and latency. We prospectively examined the relation between cigarette smoking and glioma risk among men and women in three large U.S. cohort studies: the Health Professionals Follow-up Study (HPFS), the Nurses' Health Study I (NHS), and NHS II. Information on smoking history was obtained at baseline (1986 for HPFS, 1976 for NHS, and 1989 for NHS II) and updated biennially through 2002 in the HPFS and the NHS and 2003 in the NHS II. We confirmed 110 incident gliomas among men and 255 gliomas among women during 667,673 and 4,388,515 person-years of follow-up, respectively. Cox proportional hazard models were used to estimate incidence rate ratios and 95% confidence intervals between smoking and glioma risk adjusting for age, total meat intake, and alcohol and coffee consumption. Estimates from each cohort were pooled using a random-effects model after determining that there was no heterogeneity by sex. No association with glioma risk was observed between baseline or updated smoking status, intensity, duration, or age at smoking initiation among men and women. Furthermore, no association with glioma risk was observed after allowing for an induction period between smoking and glioma diagnosis. These findings provide strong evidence that cigarette smoking is not associated with an appreciably elevated risk of adult glioma.