Background: Studies of postmenopausal hormone therapy and lung cancer incidence have reported positive, negative, and null associations. Most of these studies, however, have had limited ability to control rigorously for cigarette smoking or to examine risk separately by smoking status.
Methods: We examined the association between postmenopausal hormone therapy and lung cancer incidence by smoking status among 72,772 women in the Cancer Prevention Study II Nutrition Cohort. Proportional hazards modeling was used to calculate rate ratios (RR).
Results: During follow-up from 1992 to 2003, we identified 659 cases of incident lung cancer. Current use of any postmenopausal hormone therapy was significantly associated with decreased risk of incident lung cancer [multivariate RR, 0.76; 95% confidence interval (95% CI), 0.62-0.92]. Similar risk estimates were observed for unopposed estrogen use (RR, 0.76; 95% CI, 0.60-0.94) and for estrogen plus progestin (RR, 0.76; 95% CI, 0.57-1.01). Risk associated with current use of postmenopausal hormone therapy was decreased among never smokers (RR, 0.56; 95% CI, 0.33-0.95) as well as current smokers (RR, 0.76; 95% CI, 0.55-1.05) and former smokers (RR, 0.76; 95% CI, 0.58-0.99). Former hormone use was not associated with lung cancer. No trend with duration of hormone use was detected.
Conclusion: These results support the hypothesis that postmenopausal hormone therapy is associated with reduced risk of lung cancer, although the absence of a dose-response relationship weakens the evidence for causality.