title: Human papillomavirus infection and risk of breast cancer: a meta-analysis of case-control studies.
abstract: BACKGROUND
  Although systematic reviews (SR) report that human papillomavirus (HPV) increases the risk of breast cancer, there are still disputes regarding this association. In particular, it has been argued that the risk level differs depending on nationality, type of tissue, subtype of HPV, and publication year. Considering that the searching year of publication for the previous SRs was June 2013, a renewal meta-analysis needs to be conducted.
  
  
  METHODS
  Using articles selected in the previous SRs, we compiled a list of references, cited articles, and related articles from the PubMed and Scopus databases. Of these, only publications with data from case-control studies on HPV DNA-positivity in tissues were chosen. Summary odds ratio (SOR) and 95 % confidence interval (CI) were calculated through meta-analysis. Meta-regression analysis was performed for nationality, types of tissue, subtype of HPV, and publication year.
  
  
  RESULTS
  Twenty-two case-control studies were selected, and the total number of individuals in the case and control group was 1897 and 948, respectively. According to the meta-analysis about the 22 publications, HPV infection increased the risk of breast cancer (SOR = 4.02, 95 % CI: 2.42-6.68; I-squared = 44.7 %). Statistical significance was not found in meta-regression performed on the four variables of nationality, type of tissue, subtype of HPV, and publication year which some researchers think sources of heterogeneity.
  
  
  CONCLUSIONS
  The results of the present study supported the argument that HPV infection increases the risk of breast cancer. Age-matched case-control studies are in need in the future.
authors.affiliation: Department of Preventive Medicine, Jeju National University School of Medicine, Jejudo, South Korea.
authors.forename: Jong-Myon
authors.initials: JM
authors.lastname: Bae
authors.affiliation: Department of Preventive Medicine, Jeju National University School of Medicine, Jejudo, South Korea.
authors.forename: Eun Hee
authors.initials: EH
authors.lastname: Kim
keywords: Breast neoplasms; Human Papillomavirus; Meta-analysis; Risk factor