title: The relationship between gravidity and parity and colorectal cancer risk.
abstract: OBJECTIVE
  The influence of hormonal changes caused by pregnancy has been well studied in relation to colorectal cancer risk, but the association remains undefined. The purpose of this investigation was to examine in a case-control study the relationship between differences in gravidity and parity and colorectal cancer risk and if the association varied by microsatellite instability (MSI), a feature more common in women.
  
  
  METHODS
  The study population included incident colorectal cancer patients (n = 1014), aged 50-74 years, diagnosed in 1998-2002 in Washington state and controls (n = 1064) randomly selected from population lists. All study subjects completed telephone interviews to ascertain prior pregnancies, live births, and other covariates. Case tissue samples were obtained for MSI analyses. Multivariable logistic regression models estimated odds ratios (OR) and 95% confidence intervals (CI), adjusting for age, family history of colorectal cancer, body mass index (BMI), education, endoscopy screening, oral contraceptive use, hormone therapy use, smoking, and alcohol consumption.
  
  
  RESULTS
  There was an approximate 30%-50% reduction in risk of colon cancer associated with gravidity, which was attenuated in the analysis with parity. Increasing gravidity and parity were associated with a suggestion of a decreasing trend in risk for rectal cancer (p for trend = 0.07). Compared with women who had equal numbers of pregnancies and live births, women who were nulligravid and nulliparous had a 40%-60% increased risk of colon cancer. There was a suggestion of a reduced risk of both colon and rectal cancer associated with one more pregnancy than live birth. There was a suggestion of an increased risk of MSI-high tumors with nulligravidity and nulliparity.
  
  
  CONCLUSIONS
  These results confirm the importance of pregnancy events in the etiology of colon and rectal cancer.
authors: Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA. kwernli@fhcrc.org
authors: Karen J
authors: KJ
authors: Wernli
authors: Yinghui
authors: Y
authors: Wang
authors: Yingye
authors: Y
authors: Zheng
authors: John D
authors: JD
authors: Potter
authors: Polly A
authors: PA
authors: Newcomb
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D003110:Colonic Neoplasms / Q000453:epidemiology / Q000209:etiology*; D005260:Female; D020073:Gravidity; D006801:Humans; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D012004:Rectal Neoplasms / Q000453:epidemiology / Q000209:etiology*; D012044:Regression Analysis; D012306:Risk; D012307:Risk Factors; D012959:Socioeconomic Factors