title: Reproductive factors and lung cancer risk among women in the Singapore Breast Cancer Screening Project.
abstract: OBJECTIVE
  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.
  
  
  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.
  
  
  CONCLUSIONS
  Our findings add to the existing evidence that parous women have a lower lung cancer risk than nulliparous women.
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, Singapore; Division of Medical Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Hui Shan
authors.initials: HS
authors.lastname: Tan
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, Singapore; Division of Medical Oncology, National Cancer Centre Singapore, Singapore; Institute of Bioengineering and Nanotechnology, Singapore.
authors.forename: Min-Han
authors.initials: MH
authors.lastname: Tan
authors.affiliation: National Registry of Diseases Office, Singapore.
authors.forename: Khuan Yew
authors.initials: KY
authors.lastname: Chow
authors.affiliation: Division of Medical Oncology, National Cancer Centre Singapore, Singapore.
authors.forename: Wen Yee
authors.initials: WY
authors.lastname: Chay
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, Singapore. Electronic address: weiyenlim@gmail.com.
authors.forename: Wei-Yen
authors.initials: WY
authors.lastname: Lim
mesh_terms: D000368:Aged; D055088:Early Detection of Cancer; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008175:Lung Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D008572:Menarche; D008593:Menopause; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D016016:Proportional Hazards Models; D017584:Reproductive History; D012306:Risk; D012846:Singapore / Q000453:epidemiology; D012907:Smoking
keywords: Cohort study; Lung neoplasms; Menarche; Parity; Reproductive history