title: Diabetes mellitus and subsite-specific colorectal cancer risks in the Iowa Women's Health Study.
abstract: OBJECTIVE
  Controversy remains regarding the association between type 2 diabetes mellitus (DM) and colorectal cancer (CRC) risk. To clarify and extend the existing data, we prospectively evaluated the association between self-reported type 2 DM (onset at >30 years of age) and incident CRC, overall and by anatomic subsite, among postmenopausal women in the Iowa Women's Health Study (n = 35,230).
  
  
  METHODS
  After 14 years of follow-up, a total of 870 incident CRC cases were identified through annual linkage to the Iowa Cancer Registry. DM was analyzed as reported at baseline and as a time-dependent variable using information obtained during follow-up. CRC risks were estimated using Cox proportional hazards regression models.
  
  
  RESULTS
  After adjusting for age, body mass index and other potential confounding variables, the relative risk (RR) for women with DM versus women without DM was modestly increased at 1.4 [95% confidence interval (95% CI), 1.1-1.8]. By anatomic subsite, the RR for proximal colon cancer was statistically significantly increased (RR, 1.9; 95% CI, 1.3-2.6), whereas the RRs for distal colon (RR, 1.1; 95% CI, 0.6-1.8) and rectal cancer (RR, 0.8; 95% CI, 0.4-1.6) were not statistically different from unity. Analyses that included DM ascertained at baseline and follow-up yielded similar results.
  
  
  CONCLUSIONS
  In this large, prospective study of postmenopausal women, the association between DM and incident CRC was found to be subsite specific. If confirmed by others, this finding implies that CRC prevention strategies among type 2 DM patients should include examination of the proximal colon.
authors.affiliation: Division of Epidemiology, University of Minnesota, 1300 South Second Street, Suite 300, Minneapolis, MN 55454, USA. limburg.paul@mayo.edu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Limburg
authors.forename: Kristin E
authors.initials: KE
authors.lastname: Anderson
authors.forename: Trista W
authors.initials: TW
authors.lastname: Johnson
authors.forename: David R
authors.initials: DR
authors.lastname: Jacobs
authors.forename: Deann
authors.initials: D
authors.lastname: Lazovich
authors.forename: Ching-Ping
authors.initials: CP
authors.lastname: Hong
authors.forename: Kristin K
authors.initials: KK
authors.lastname: Nicodemus
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Folsom
mesh_terms: D017668:Age of Onset; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000209:etiology*; D048909:Diabetes Complications; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D007484:Iowa / Q000453:epidemiology; D008875:Middle Aged; D017698:Postmenopause; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012042:Registries; D012307:Risk Factors