Suh M, Wikoff D, Harvey S, Mittal L, Lipworth L, Goodman M, Goodmanson A, Ring C, Rohr A, Proctor D. Hexavalent chromium and stomach cancer: A systematic review and meta-analysis. Presented at Joint Annual Meeting of International Society of Exposure Science and International Society for Environmental Epidemiology (ISES-ISEE 2018), Ottawa, Canada, August 2018.
Hexavalent chromium [Cr(VI)] is a carcinogen known to cause lung cancer in workers of certain industries. An association with stomach cancer is uncertain. Systematic review and metaanalyses were conducted to evaluate the association between Cr(VI) and risk of stomach cancer. Documented in the protocol (PROSPERO #CRD4201605162), PubMed, Embase®, and hand searching were used to identify studies. Eligibility criteria included studies of: 1) animals with ingestion exposures to Cr(VI) (n=3); 2) non-occupational populations with ingestion exposures to Cr(VI) (n=6); 3) workers in occupations recognized as having exposure to Cr(VI) (n=50; 3 case-control, 47 cohort). Critical appraisal and qualitative integration were carried out using the National Toxicology Program’s Office of Health Assessment and Translation approach; 9 meta-analyses were conducted based on the occupational data. Of the animal studies, one study with low risk of bias was negative, one study with high risk of bias reported forestomach tumors but showed poor internal validity; another study was negative. Non-occupational data were ecologic studies with conflicting results; they were unsuitable for meta-analysis. Critical appraisal of the occupational data with regards to internal validity showed that most studies were categorized as Tier 3 (n=37) or Tier 2 (n=12) with high or probably high risk of bias observed for confounding and exposure characterization domains; overall confidence in this body of evidence was moderate. Meta-analyses consistently showed no significantly increased stomach cancer risk. The overall meta-relative risk (meta RR, excluding Tier 3 studies) for stomach cancer was 1.03 (95%CI 0.84-1.26). Notably, for studies of workers (n=22) from industries with clear evidence of elevated lung cancer due to Cr(VI) exposure, meta-RR was not significantly elevated (1.07, 95%CI 0.89-1.27). Combining the streams of evidence, a lack of association between Cr(VI) and stomach cancer is shown.