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). CONCLUSION: Our findings indicate that metformin therapy is not significantly associated with lower prostate cancer risk.
ABSTRACT
BACKGROUND: The relationship of vasectomy to prostate cancer has great public health significance. However, the results of observational studies were conflicting. To determine whether vasectomy is associated with the risk of prostate cancer, we performed a meta-analysis of cohort studies. METHODS: A literature search was carried out using Pubmed, Embase, Cochrane Libraryl, and China National Knowledge Infrastructure (CNKI) between January 1966 and July 2013. Before meta-analysis, between-study heterogeneity and publication bias were assessed using adequate statistical tests. Fixed-effect and random-effect models were used to estimate summary relative risks (RR) and the corresponding 95% confidence intervals (CIs). Potential sources of heterogeneity were detected by meta-regression. Subgroup analyses and sensitivity analysis were also performed. RESULTS: A total of nine cohort studies contributed to the analysis. There was heterogeneity among the studies but no publication bias. Pooled results indicated that vasectomy was not associated with a significant increase of total prostate cancer risk (RR = 1.07, 95% CI [0.79, 1.46]). When stratified the various studies by geographic location, we found a significant association between vasectomy and increased PCa risk among studies conducted in the USA (RR = 1.54, 95% CI [1.23, 1.93]), however, there was no significant association between vasectomy and PCa risk among studies conducted in non-USA countries (RR = 0.74, 95% CI [0.50, 1.09]). Furthermore, sensitivity analysis confirmed the stability of the results. CONCLUSIONS: In conclusion, the present meta-analysis of cohort studies suggested that vasectomy was not associated with increased risk of prostate cancer. More in-depth studies are warranted to report more detailed results, including stratified results by age at vasectomy, tumor grade, and tumor stage.
