title: Reproductive factors and risk of oesophageal and gastric cancer in the Million Women Study cohort.
abstract: BACKGROUND
  Hormonal factors may influence risk for upper gastrointestinal cancers in women. We examined risk of oesophageal and gastric cancers in relation to reproductive factors in a large UK cohort, the Million Women Study.
  
  
  METHODS
  Among 1,319,409 women aged on average 56 years at recruitment, 1186 incident cancers of the oesophagus and 1194 of the stomach were registered during 11.9 million person-years' observation. Adjusted relative risks (RRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards models.
  
  
  RESULTS
  Risks of both oesophageal and gastric cancer were significantly higher in postmenopausal than in pre- or peri-menopausal women (RRs 1.46, 1.07-2.00 and 1.59, 1.15-2.20, respectively; P≤0.01 for both); and, among postmenopausal women, risk was higher the younger women were at menopause (RR, 95% CI per 5 years younger at menopause 1.18, 1.05-1.34 for oesophageal cancer and 1.18, 1.04-1.34 for stomach cancer, P(trend)=0.01 for both). For factors relating to childbearing, including women's age at first birth, their number of children, and breastfeeding history, the only significant association was a higher risk of oesophageal cancer in nulliparous, compared with parous, women (RR 1.31, 1.11-1.55; P=0.002). When risks for squamous cell and adenocarcinomas of the oesophagus were compared, most did not differ significantly, but statistical power was limited.
  
  
  CONCLUSIONS
  Both oesophageal and gastric cancer risks appeared to be related to menopausal status and age at menopause, but there was little consistent evidence for associations with factors related to childbearing.
authors: Cancer Epidemiology Unit, University of Oxford, Richard Doll Building, Roosevelt Drive, Oxford OX3 7LF, UK. jane.green@ceu.ox.ac.uk
authors: J
authors: J
authors: Green
authors: A
authors: A
authors: Roddam
authors: K
authors: K
authors: Pirie
authors: O
authors: O
authors: Kirichek
authors: G
authors: G
authors: Reeves
authors: V
authors: V
authors: Beral
mesh_terms: D015331:Cohort Studies; D004938:Esophageal Neoplasms / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008875:Middle Aged; D012098:Reproduction; D012307:Risk Factors; D013274:Stomach Neoplasms / Q000503:physiopathology*