Meta-analysis of hexavalent chromium exposure and stomach cancer

Regulatory agencies and the scientific community acknowledge that exposure to hexavalent chromium (Cr(VI)) can cause lung cancer, but data from human studies regarding its link to stomach cancer are more limited. This is not only important in workers who may inhale Cr(VI), but also for people who may ingest Cr(VI) in drinking water, since recent data in laboratory animals have linked ingested Cr(VI) to gastrointestinal cancers. Because the highest exposures to chemicals occur in workplaces and because workplace exposures are often well studied, we looked at occupational exposure to Cr(VI)and occurrence of stomach cancer in the exposed populations. We performed a systematic review of the literature and selected studies of workers and occupations routinely exposed to Cr(VI). We conducted a meta-analysis of 39 cohort and case-control studies that reported results for non-respiratory cancers including stomach cancer. Where the paper presented more than one measure of incidence or mortality, we selected the effect measure for the most highly exposed group. Meta-analysis of the findings for stomach cancer yielded a preliminary summary relative risk (RR) of 1.31, 95% CI=1.18-1.45. In studies in which lung cancer relative risks were elevated, the summary stomach cancer RR was even higher (RR=1.36, 95% CI=1.12-1.65). Overall, these results suggest that Cr(VI) is a stomach carcinogen in humans and support findings from animal and other human studies linking chromium to cancer of the gastrointestinal tract.