title: A meta-analysis of asbestos and lung cancer: is better quality exposure assessment associated with steeper slopes of the exposure-response relationships?
abstract: BACKGROUND
  Asbestos is a well-recognized cause of lung cancer, but there is considerable between-study heterogeneity in the slope of the exposure-response relationship.
  
  
  OBJECTIVE
  We considered the role of quality of the exposure assessment to potentially explain heterogeneity in exposure-response slope estimates.
  
  
  METHODS
  We searched PubMed MEDLINE (1950-2009) for studies with quantitative estimates of cumulative asbestos exposure and lung cancer mortality and identified 19 original epidemiological studies. One was a population-based case-control study, and the others were industry-based cohort studies.
  
  
  METHODS
  Cumulative exposure categories and corresponding risks were abstracted. Exposure-response slopes [KL (lung cancer potency factor of asbestos)] were calculated using linear relative risk regression models.
  
  
  RESULTS
  We assessed the quality of five exposure assessment aspects of each study and conducted random effects univariate and multivariate meta-regressions. Heterogeneity in exposure-response relationships was greater than expected by chance (I2 = 64%). Stratification by exposure assessment characteristics revealed that studies with well-documented exposure assessment, larger contrast in exposure, greater coverage of the exposure history by exposure measurement data, and more complete job histories had higher meta-KL values than did studies without these characteristics. The latter two covariates were most strongly associated with the KL value. Meta-KL values increased when we incrementally restricted analyses to higher-quality studies.
  
  
  CONCLUSIONS
  This meta-analysis indicates that studies with higher-quality asbestos exposure assessment yield higher meta-estimates of the lung cancer risk per unit of exposure. Potency differences for predominantly chrysotile versus amphibole asbestos-exposed cohorts become difficult to ascertain when meta-analyses are restricted to studies with fewer exposure assessment limitations.
authors.affiliation: Institute for Risk Assessment Sciences, Division of Environmental Epidemiology, Utrecht University, Utrecht, The Netherlands.
authors.forename: Virissa
authors.initials: V
authors.lastname: Lenters
authors.forename: Roel
authors.initials: R
authors.lastname: Vermeulen
authors.forename: Sies
authors.initials: S
authors.lastname: Dogger
authors.forename: Leslie
authors.initials: L
authors.lastname: Stayner
authors.forename: Lützen
authors.initials: L
authors.lastname: Portengen
authors.forename: Alex
authors.initials: A
authors.lastname: Burdorf
authors.forename: Dick
authors.initials: D
authors.lastname: Heederik
mesh_terms: D017636:Asbestos, Amphibole / Q000633:toxicity*; D017632:Asbestos, Serpentine / Q000633:toxicity*; D002274:Carcinogens, Environmental / Q000633:toxicity*; D016022:Case-Control Studies; D015331:Cohort Studies; D008175:Lung Neoplasms / Q000139:chemically induced / Q000453:epidemiology* / Q000401:mortality; D016273:Occupational Exposure; D012107:Research Design; D018570:Risk Assessment
chemical_list: D017636:Asbestos, Amphibole; D017632:Asbestos, Serpentine; D002274:Carcinogens, Environmental