title: Diabetes, metformin use, and colorectal cancer survival in postmenopausal women.
abstract: BACKGROUND
  Observational studies have associated metformin use with lower colorectal cancer (CRC) incidence but few studies have examined metformin's influence on CRC survival. We examined the relationships among metformin use, diabetes, and survival in postmenopausal women with CRC in the Women's Health Initiative (WHI) clinical trials and observational study.
  
  
  METHODS
  2066 postmenopausal women with CRC were followed for a median of 4.1 years, with 589 deaths after CRC diagnosis from all causes and 414 deaths directly attributed to CRC. CRC-specific survival was compared among women with diabetes with metformin use (n=84); women with diabetes with no metformin use (n=128); and women without diabetes (n=1854). Cox proportional hazard models were used to estimate associations among metformin use, diabetes and survival after CRC. Strategies to adjust for potential confounders included: multivariate adjustment with known predictors of colorectal cancer survival and construction of a propensity score for the likelihood of receiving metformin, with model stratification by propensity score quintile.
  
  
  RESULTS
  After adjusting for age and stage, CRC specific survival in women with diabetes with metformin use was not significantly different compared to that in women with diabetes with no metformin use (HR 0.75; 95% CI 0.40-1.38, p=0.67) and to women without diabetes (HR 1.00; 95% CI 0.61-1.66, p=0.99). Following propensity score adjustment, the HR for CRC-specific survival in women with diabetes with metformin use compared to non-users was 0.78 (95% CI 0.38-1.55, p=0.47) and for overall survival was 0.86 (95% CI 0.49-1.52; p=0.60).
  
  
  CONCLUSIONS
  In postmenopausal women with CRC and DM, no statistically significant difference was seen in CRC specific survival in those who used metformin compared to non-users. Analyses in larger populations of colorectal cancer patients are warranted.
authors.affiliation: Tufts Medical Center, 800 Washington Street, Box 245, Boston, MA 02111, USA. fcossor@tuftsmedicalcenter.org
authors.forename: Furha Iram
authors.initials: FI
authors.lastname: Cossor
authors.forename: Lucile L
authors.initials: LL
authors.lastname: Adams-Campbell
authors.forename: Rowan T
authors.initials: RT
authors.lastname: Chlebowski
authors.forename: Marc J
authors.initials: MJ
authors.lastname: Gunter
authors.forename: Karen
authors.initials: K
authors.lastname: Johnson
authors.forename: Robert E
authors.initials: RE
authors.lastname: Martell
authors.forename: Anne
authors.initials: A
authors.lastname: McTiernan
authors.forename: Michael S
authors.initials: MS
authors.lastname: Simon
authors.forename: Thomas
authors.initials: T
authors.lastname: Rohan
authors.forename: Robert B
authors.initials: RB
authors.lastname: Wallace
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Paulus
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology / Q000401:mortality*; D003920:Diabetes Mellitus / Q000188:drug therapy / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007004:Hypoglycemic Agents / Q000008:administration & dosage; D053208:Kaplan-Meier Estimate; D008687:Metformin / Q000008:administration & dosage*; D008875:Middle Aged; D017698:Postmenopause; D016032:Randomized Controlled Trials as Topic; D014481:United States / Q000453:epidemiology
chemical_list: D007004:Hypoglycemic Agents; D008687:Metformin
keywords: Colorectal neoplasm; Diabetes mellitus; Female; Metformin; Survival rate; Treatment outcome