• Gang-Feng Wu, Xiao-Long Zhang, Zhen-Gang Luo, Jia-Jun Yan, Shou-Hua Pan, Xiang-Rong Ying, Jian-Gang Pan, and Guan-Fu Zhang.
• Department of Urology, Shaoxing People's Hospital, Shaoxing Hospital of Zhejiang University Shaoxing, Zhejiang, China.
• Int J Clin Exp Med. 2015 Jan 1; 8 (8): 13089-98.

ObjectiveSeveral 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.MethodsWe 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.ResultsWe 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).ConclusionOur findings indicate that metformin therapy is not significantly associated with lower prostate cancer risk.

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