title: Vasectomy and the risk of prostate cancer: a meta-analysis of cohort studies.
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.
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: 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: 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: 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: Guan-Fu
authors.initials: GF
authors.lastname: Zhang
keywords: Vasectomy; meta-analysis; prostate cancer; risk