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Common solvent linked to liver cancer risk

By Kathryn Doyle

NEW YORK (Reuters Health) - Scandinavian workers exposed to a common industrial cleaning fluid showed higher risk for developing cancers of the liver, kidneys and cervix in a large new study.

Trichloroethylene, or TCE, is a chemical solvent that has already been shown to cause cancer in animals when inhaled or absorbed through the skin in large amounts.

The World Health Organization designated TCE a human carcinogen in October 2012, but the chemical is still used widely in industry to clean machinery and in some etching processes, at levels believed to be too low to harm people.

The WHO flagged TCE as particularly dangerous to the kidneys, but past studies have also suggested links to cancers of the liver, kidney, cervix and esophagus as well as non-Hodgkin lymphoma.

"Our study and other studies indicate that the relative risk of kidney cancer is modest, and perhaps high levels are needed to cause kidney cancer," said Johnni Hansen of the Danish Cancer Society Research Center in Copenhagen, who led the new study.

In the Nordic countries examined for the study, levels of TCE used in industrial settings are very low compared to other countries like the U.S., perhaps too low to be linked to an increased risk to kidneys, Hansen told Reuters Health by email.

Hansen and his colleagues updated and analyzed data from three previous studies in Sweden, Finland and Denmark, which included 5,553 workers (1,777 of them women) with documented exposure to TCE. The researchers had records from cancer registries starting in 1958 and results from urine tests tracking the workers' TCE exposure levels from 1947 to 1989.

Based on rates of liver cancer in the general population in the three countries, the researchers expected to see 20 liver cancer cases among the workers over the study period, but actually saw 36 cases. Similarly, they expected to see two cases of cervical cancer, but actually saw seven.

The overall risk for either of the two cancers was still very small, Hansen noted.

And the 32 cases of kidney cancer diagnosed among the workers is the same number that would be expected in the general population, the team reports in the Journal of the National Cancer Institute.

The study has strengths and weaknesses, experts said. Knowing with some level of certainty that each person had been exposed to TCE, based on urine tests, was a step up from previous studies, according to Hansen.

Elizabeth Ward, an epidemiologist at the American Cancer Society in Atlanta agreed. "This study is exceptionally strong because historical measurements of a trichloroethylene metabolite in humans are available to document the exposure," said Ward, who was not involved in the study.

The research did not, however, include information on the workers' histories of smoking or drinking alcohol, which are also known to raise cancer risk, and the number of subjects included was relatively small for a study of this kind.

Not finding a link to kidney cancer doesn't discount the study as a whole, nor the WHO classification of the chemical as a cause of kidney cancer, according to Mark Purdue at the Division of Cancer Epidemiology and Genetics of the National Cancer Institute in Bethesda, Maryland.

"The small size of the study reduced the investigators' chances of detecting small associations such as those observed for kidney cancer and non-Hodgkin lymphoma," said Purdue, who wrote an editorial accompanying the study.

TCE is still used in the U.S. at levels regulated by the Occupational Safety and Health Administration as an intermediate step in the production of refrigerant chemicals and for cleaning metal parts. Workers most often inhale the chemical, Purdue said, but it can be absorbed through skin.

TCE contamination of drinking and bathing water supplies has led to multiple lawsuits in the U.S. and a specially commissioned report in 2006 from the National Research Council (see NRC report here: http://bit.ly/122RT8V).

But Ward told Reuters Health, "The increased risks found in this study would apply to people occupationally exposed and not the general population."

Source: Journal of the National Cancer Institute http://bit.ly/14l1O5R, online May 30, 2013.

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