Cigarette smoking and subsequent risk of lung cancer in men and women: analysis of a prospective cohort study.

BACKGROUND: Whether women are more susceptible than men to lung cancer caused by cigarette smoking has been controversial. To address this question, we aimed to compare incidence rates of lung cancer by stratum of smoking use in men and women of the National Institutes of Health (NIH)-AARP cohort.
METHODS: Participants in the NIH-AARP Diet and Health study responded to a postal questionnaire between Oct 13, 1995, and May 6, 1996, and were followed up until Dec 31, 2003. The questionnaire asked participants about their past and current smoking status, demographics, alcohol intake, tobacco smoking, physical activity, and included a food-frequency questionnaire of 124 items. Incident lung cancers were identified by linkage to individual state cancer registries. We present age-standardised incidence rates for cancer and multivariate hazard ratios (HRs) adjusted for potential confounders, with 95% CIs. This study conforms to the STROBE guidelines.
FINDINGS: 279 214 men and 184 623 women from eight states in the USA aged 50-71 years at study baseline were included in this analysis. During follow-up, lung cancers occurred in 4097 men and 2237 women. Incidence rates were 20.3 (95% CI 16.3-24.3) per 100 000 person-years in men who had never smoked (99 cancers) and 25.3 (21.3-29.3) in women who had never smoked (152 cancers); for this group, the adjusted HR for lung cancer was 1.3 (1.0-1.8) for women compared with men. Smoking was associated with increased risk of lung cancer in men and women. The incidence rate of current smokers who smoked more than two packs per day was 1259.2 (1035.0-1483.3) in men and 1308.9 (924.2-1693.6) in women. In current smokers, in a model adjusted for typical smoking dose, the HR was 0.9 (0.8-0.9) for women compared with men. For former smokers, in a model adjusted for years of cessation and typical smoking dose, the HR was 0.9 (0.9-1.0) for women compared with men. Incidence rates of adenocarcinoma, small-cell carcinoma, and undifferentiated tumours were similar in men and women; incidence rates of squamous tumours in men were about twice that in women.
INTERPRETATION: Our findings suggest that women are not more susceptible than men to the carcinogenic effects of cigarette smoking in the lung. In smokers, incidence rates tended to be higher in men than women with comparable smoking histories, but differences were modest; smoking was strongly associated with lung cancer risk in both men and women. Future studies should confirm whether incidence rates are indeed higher in women who have never smoked than in men who have never smoked.