title: Secondhand smoking, 4-aminobiphenyl, and bladder cancer: two meta-analyses.
abstract: OBJECTIVE
  To quantify the relation between secondhand smoking (SHS) and levels of 4-aminobiphenyl (4-ABP; in urine or blood) and SHS and bladder cancer risk in nonsmokers.
  
  
  METHODS
  PubMed and Embase were searched (search terms to represent SHS, bladder cancer, and 4-ABP) to conduct two meta-analyses. Information about gender and age of participants, mean 4-ABP level for each SHS category, number of subjects, relative risk or odds ratio and 95% confidence intervals (95% CI) in each SHS category, and covariates for which adjustment was made was extracted based on predefined inclusion and exclusion criteria. Random-effects analyses were done using STATA (version 9).
  
  
  RESULTS
  A 118 studies were reviewed for information on SHS and 4-ABP (31 studies) and SHS and bladder cancer risk (87 studies). Of those, seven case-control studies were included for analysis of SHS and 4-ABP and eight articles (three cohort and five case-control studies) for SHS and bladder cancer risk. A random-effects model found a pooled standardized mean difference of 1.47 (95% CI, 0.23-2.71), indicating higher levels of 4-ABP among nonsmokers exposed to SHS. A random-effects model showed no evidence for an association between SHS and bladder cancer risk (relative risk, 0.99; 95% CI, 0.86-1.14), comparing nonsmokers with and without SHS exposure.
  
  
  CONCLUSIONS
  Higher levels of 4-ABP were significantly associated with SHS exposure, which is consistent with earlier findings for 4-ABP levels in sidestream smoke. The current evidence indicates that there is no association between SHS and bladder cancer, but future studies that address methodologic limitations are needed to further clarify this important question.
authors.affiliation: Division of Cancer Studies, King's College London, Research Oncology, London SE1 9RT, UK. mieke.vanhemelrijck@kcl.ac.uk.
authors.forename: Mieke J J
authors.initials: MJ
authors.lastname: Van Hemelrijck
authors.forename: Dominique S
authors.initials: DS
authors.lastname: Michaud
authors.forename: Gregory N
authors.initials: GN
authors.lastname: Connolly
authors.forename: Zubair
authors.initials: Z
authors.lastname: Kabir