title: Reproductive history and risk of colorectal cancer in postmenopausal women.
abstract: BACKGROUND
  There are conflicting data regarding the role of sex hormones in colorectal cancer development. Whereas clinical trials data indicate that hormone therapy use reduces the risk of colorectal cancer, data from prospective cohort studies suggest that circulating estrogen levels are positively associated with colorectal cancer risk. A surrogate measure of lifetime estrogen exposure is reproductive history. We investigated the relationship between reproductive factors and the risk of colorectal cancer.
  
  
  METHODS
  Subjects were postmenopausal women enrolled in the National Institutes of Health-American Association of Retired Persons Diet and Health Study, a cohort of 214,162 individuals (aged 50-71 years) that included 2014 incident cases of colorectal cancer that occurred over a mean follow-up of 8.2 years. Questionnaires were used to collect data on reproductive factors, including ages at menarche, birth of first child, and menopause; parity, and use of oral contraceptives. Multivariable Cox proportional hazards models were constructed to examine associations between these reproductive factors and the risk of colorectal cancer, with adjustment for established colorectal cancer risk factors. All statistical tests were two-sided.
  
  
  RESULTS
  Age at menopause (≥ 55 vs < 40 years: hazard ratio [HR] = 1.50, 95% confidence interval [CI] = 1.23 to 1.83; P(trend) = .008) and age at birth of first child (≥ 30 vs ≤ 19 years: HR = 1.26, 95% CI = 1.01 to 1.58; P(trend) = .05) were positively associated with the risk of colorectal cancer. Among women with no history of hormone therapy use, age at menarche (≥ 15 vs 11-12 years: HR = 0.73, 95% CI = 0.57 to 0.94; P(trend) = .02) and parity (≥ 5 children vs no children: HR = 0.80, 95% CI = 0.63 to 1.02; P(trend) = .10) were inversely associated with the risk of colorectal cancer.
  
  
  CONCLUSIONS
  These data support a role for sex hormones in colorectal tumorigenesis and suggest that greater endogenous estrogen exposure may increase the risk of colorectal cancer in postmenopausal women.
authors: Department of Oncology, Montefiore Medical Center, Bronx, NY, USA.
authors: Alice
authors: A
authors: Zervoudakis
authors: Howard D
authors: HD
authors: Strickler
authors: Yikyung
authors: Y
authors: Park
authors: Xiaonan
authors: X
authors: Xue
authors: Albert
authors: A
authors: Hollenbeck
authors: Arthur
authors: A
authors: Schatzkin
authors: Marc J
authors: MJ
authors: Gunter
mesh_terms: D000367:Age Factors; D000368:Aged; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology; D015914:Estrogen Replacement Therapy / Q000009:adverse effects* / Q000706:statistics & numerical data; D004967:Estrogens / Q000009:adverse effects*; D005260:Female; D006801:Humans; D008572:Menarche; D008875:Middle Aged; D015999:Multivariate Analysis; D016017:Odds Ratio; D036801:Parturition; D017698:Postmenopause; D016016:Proportional Hazards Models; D011446:Prospective Studies; D017584:Reproductive History; D018570:Risk Assessment; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology
chemical_list: D004967:Estrogens