Reproductive factors and lung cancer risk among women in the Singapore Breast Cancer Screening Project

Objectives: A growing body of literature suggests that female hormones play a role in lung cancer risk. Our study aims to examine the relationship between reproductive factors and lung cancer incidence in a large prospectively enrolled cohort in Singapore. Materials and Methods: Multivariate Cox proportional hazard regression models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) of lung cancer for each exposure, adjusting for smoking, age at entry, ethnicity and body mass index. Results: Among 28,222 women aged 50-64 years enrolled in the Singapore Breast Cancer Screening Project from October 1994 to February 1997, we identified 311 incident lung cancer cases (253 in non-smokers) over an average of 15.8 years of follow-up to 31 December 2011. Higher parity was associated with decreased lung cancer risk. Compared with nulliparous women, those with 1-2, 3-4, and >= 5 deliveries had a hazard ratio (HR) of 0.56, 0.55 and 0.45, respectively (P-trend <0.01). This association was observed in both smokers and non-smokers, and in both adenocarcinomas and non-adenocarcinomas. Reproductive period, breastfeeding, oral contraceptive and hormone replacement therapy use did not seem to influence the risk of getting lung cancer. Conclusion: Our findings add to the existing evidence that parous women have a lower lung cancer risk than nulliparous women. (c) 2015 Elsevier Ireland Ltd. All rights reserved.