title: Metformin therapy and prostate cancer risk: a meta-analysis of observational studies.
abstract: OBJECTIVE
  Several observational studies have shown that metformin therapy may modify the risk of prostate cancer. We carried out a meta-analysis of relevant studies evaluating the effect of metformin therapy on prostate cancer risk.
  
  
  METHODS
  We searched pubmed database (January 1966-February 2014) for case-control and cohort studies that assessed metformin therapy and prostate cancer risk. Two authors independently assessed eligibility and extracted data. Summary RRs was calculated using fixed-effects model or random-effects model. Heterogeneity among studies was examined using Q and I(2) statistics.
  
  
  RESULTS
  We included six cohort studies and four case-control studies in the present meta-analysis, comprising 863,769 participants and 39,073 prostate cancer cases. The pooled RR of prostate cancer in relation to metformin therapy was 0.92 (95% CI: 0.84-1.02, P = 0.112). When we stratified the various studies by study type, we found that metformin therapy was associated with a significant reduced risk of prostate cancer among cohort studies (RR = 0.92, 95% CI [0.87, 0.96], P<0.001); however, no significant association was detected among case-control studies (RR = 0.95, 95% CI [0.78, 1.16], P = 0.632). There was also no indication of publication bias as suggested by Begg's test (P = 0.421) and Egger's test (P = 0.627).
  
  
  CONCLUSIONS
  Our findings indicate that metformin therapy is not significantly associated with lower prostate cancer risk.
authors.affiliation: Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
authors.forename: Gang-Feng
authors.initials: GF
authors.lastname: Wu
authors.affiliation: Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
authors.forename: Xiao-Long
authors.initials: XL
authors.lastname: Zhang
authors.affiliation: Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
authors.forename: Zhen-Gang
authors.initials: ZG
authors.lastname: Luo
authors.affiliation: Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
authors.forename: Jia-Jun
authors.initials: JJ
authors.lastname: Yan
authors.affiliation: Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
authors.forename: Shou-Hua
authors.initials: SH
authors.lastname: Pan
authors.affiliation: Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
authors.forename: Xiang-Rong
authors.initials: XR
authors.lastname: Ying
authors.affiliation: Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
authors.forename: Jian-Gang
authors.initials: JG
authors.lastname: Pan
authors.affiliation: Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
authors.forename: Guan-Fu
authors.initials: GF
authors.lastname: Zhang
keywords: Metformin; meta-analysis; observational studies; prostate cancer; risk