title: Occupational exposure to hexavalent chromium and cancers of the gastrointestinal tract: a meta-analysis.
abstract: BACKGROUND
  We conducted a systematic literature review and meta-analysis of oral cavity, esophageal, stomach, small intestine, colon, and rectal cancers among workers occupationally exposed to Cr(VI).
  
  
  METHODS
  Using PubMed, studies published from 1950 to 2009 evaluating the relationship between Cr(VI) exposure and GI cancers were identified. Measures of effect and variability were extracted from 32 studies meeting specific inclusion criteria, and meta-analysis summary relative risk measures were calculated using random effects models and inverse variance weighting methods.
  
  
  RESULTS
  Meta-standardized mortality ratios (SMRs) were, for cancer of the: oral cavity [1.02 (95% CI=0.77-1.34)]; esophagus [1.17 (95% CI=0.90-1.51)]; stomach [1.09 (95% CI=0.93-1.28)]; colon [0.89 (95% CI=0.70-1.12)]; and rectum [1.17 (95% CI=0.98-1.39)]. Analyses of more highly exposed subgroups included in the studies or subgroups based on geographic region or by industry with recognized Cr(VI) exposures (welding, chrome plating, chromate production, and pigment production) did not result in elevated meta-SMRs except for esophageal cancer among US cohorts [meta-SMR=1.49 (95% CI=1.06-2.09)]. However, that finding was based on a subgroup of only four studies, one of which was a PMR study. Potential confounding by socioeconomic status (SES), diet and/or smoking, or limitations due to the healthy-worker effect (HWE) were evaluated, and while smoking, diet and SES may be important factors that may have upwardly biased the meta-SMRs, HWE is not likely to have significantly affected the summary results. None of three studies reporting small intestine cancers observed a statistically significant increased risk.
  
  
  CONCLUSIONS
  These meta-analyses and literature review indicate that Cr(VI)-exposed workers are not at a greater risk of GI cancers than the general population.
authors.affiliation: ToxStrategies, Inc., Rancho Santa Margarita, CA, USA. ngatto@toxstrategies.com
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Gatto
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kelsh
authors.forename: Diem Ha
authors.initials: DH
authors.lastname: Mai
authors.forename: Mina
authors.initials: M
authors.lastname: Suh
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Proctor
mesh_terms: D002274:Carcinogens, Environmental / Q000009:adverse effects*; D002857:Chromium / Q000009:adverse effects*; D005770:Gastrointestinal Neoplasms / Q000139:chemically induced / Q000453:epidemiology*; D006801:Humans; D016273:Occupational Exposure / Q000009:adverse effects*; D012307:Risk Factors; D014481:United States / Q000453:epidemiology
chemical_list: D002274:Carcinogens, Environmental; D002857:Chromium; C074702:chromium hexavalent ion