Naturally Occurring Asbestos Linked To Lung Cancer


2005-09-05 17:43

Mesothelioma Cancer

Largest study to examine the question finds a clear link to malignant mesothelioma

Everyday exposure to naturally occurring asbestos increases the risk of developing malignant mesothelioma, according to a study by UC Davis researchers.

The study, the largest to examine the question, will be published this fall in the American Journal of Respiratory and Critical Care Medicine.

Exposure to asbestos in the workplace, particularly in shipyards, has long been recognized as a risk factor for mesothelioma, a rare form of cancer affecting the lining of the lung. But in the new study, researchers found a consistent and dose-dependent association between mesothelioma and residential proximity to ultramafic rock, the predominant source of naturally occurring asbestos.

"Our findings indicate that the risks from exposure to naturally occurring asbestos, while low, are real and should be taken seriously," said Marc Schenker, professor and chair of the UC Davis Department of Public Health Sciences and the study's senior author. "This study provides important supportive evidence that naturally occurring asbestos causes mesothelioma - and public efforts should now shift to understanding the risk and how we can protect people from this preventable malignancy."

To put the mesothelioma risk in perspective, the disease is responsible for about the same number of lung cancer deaths each year as passive smoking. About 2,500 people a year die from mesothelioma in the United States, according to National Institute of Occupational Safety and Health statistics. About 3,000 deaths from lung cancer are attributed to exposure to secondhand tobacco smoke each year, according to U.S. Environmental Protection Agency statistics.

Ultramafic rock is distributed throughout the Sierra Nevada, Coast Ranges and Klamath Mountains in Northern and Central California, and has been a source of increasing concern as new housing developments cut through these areas. Of most concern are the areas of ultramafic rock associated with tremolite asbestos.

In their ambitious study, Schenker and his colleagues used California Cancer Registry data to identify 2,908 cases of malignant mesothelioma diagnosed between 1988 and 1997 in adults ages 35 and older. In most cases, the registry also provided occupational history. As a control group, an equal number of age- and gender-matched pancreatic cancer cases was selected (since pancreatic cancer has no known association to asbestos exposure). For both the mesothelioma and pancreatic cancer cases, the researchers employed sophisticated geographic information system mapping to pinpoint home or street addresses for every diagnosed individual. A map from the California Department of Conservation, Division of Mines and Geology, served as the reference for ultramafic rock deposits. Finally, statistical adjustments were made for sex, occupational asbestos exposure and age at diagnosis.

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