NEW YORK - High arsenic levels in drinking water are already thought to raise the risk of bladder cancer, but new research suggests heavy exposure may also cause bladder tumors to be more aggressive.

A study of bladder cancer patients in Argentina and Chile found that those whose drinking water contained high levels of arsenic tended to have more chromosome abnormalities in their tumors, Reuters news service reported.

These genetic alterations were also associated with later-stage and more-quickly growing tumors, according to findings published in the 20
November issue of the Journal of the National Cancer Institute, according to Reuters.

All of this suggests that bladder tumors in people with high arsenic exposure "may behave more aggressively" than those of patients with lower
exposure, reported Dr. Lee E. Moore, of the National Cancer Institute in Bethesda, MD, and her colleagues, the news service said.

Reuters reported that in the current study, Moore's team examined tumor samples from 123 patients who had been exposed to arsenic in their drinking water.

Moore's team found that the average number of chromosome abnormalities per tumor went up in tandem with patients' arsenic exposure, according to the report.

For those in the two lower-exposure groups, there were five to six alterations per tumor, on average. Patients with the highest arsenic
exposure showed nine chromosome alterations per tumor, on average, Reuters reported.