Invited commentary: arsenic and cancer of the urinary tract.

Inorganic arsenic in drinking water is a recognized cause of cancers of the skin, lung, and bladder. In the absence of an animal model for studying arsenic carcinogenesis, epidemiologic studies provide the only quantitative data for guiding risk assessment at levels that commonly occur in drinking water. To date, most estimates of risk at low and moderate levels of exposure (<200 microg/liter) have been based on extrapolation from ecologic studies of populations exposed to much higher levels. Epidemiologic data from the prospective cohort study by Chiou et al. that appears in this issue of the JOURNAL: (Am J Epidemiol 2001;153:411-18) make an important contribution to improving the precision of the estimated risk of transitional cell carcinoma of the urinary tract associated with ingested arsenic from drinking water. The great strength of the study derives from having individually based measures of exposure and cancer diagnoses. Arsenic in water is a topic of great concern and controversy, and epidemiologic studies will continue to provide crucial information about the risks of cancer and other diseases associated with ingested arsenic.