Female reproductive factors and the risk of lung cancer in postmenopausal women: a nationwide cohort study

BACKGROUND: Reproductive factors and hormone use in postmenopausal women have been hypothesised to affect the risk of developing lung cancer, but the epidemiological evidence is inconsistent. METHODS: Using the Korean National Health Insurance System database, we identified 4,775,398 postmenopausal women older than 40 years who had undergone both cardiovascular health- and cancer screening between 1 January 2009 and 31 December 2014. Information about reproductive factors was obtained from a self-administered questionnaire. The risk of lung cancer was estimated using Cox proportional hazard regression models. RESULTS: During a median follow-up of 4.4 years, 16,556 women (15,223 non-smokers) were diagnosed with lung cancer. The risk of lung cancer was not significantly influenced by early menarche age (adjusted hazard ratio [aHR] 1.03 for menarche ≥18 vs. ≤14; 95% confidence interval [CI], 0.98–1.09) or late age at menopause (aHR 1.02 for menopause ≥55 vs. <40; 95% CI, 0.91–1.14). Furthermore, the number of children, duration of breastfeeding and use of hormone replacement therapy were not associated with the risk of lung cancer. CONCLUSIONS: No statistically significant association was found between reproductive factors and the risk of lung cancer in postmenopausal Korean women.