Minnesota Department of Health has identified six additional cases of mesothelioma in a group of 72,000 people who worked in the state's iron mining industry between the 1930s and 1982.
Discovery of the six new cases brings the total number diagnosed in the workers to 58. MDH officials learned about the new cases as they reviewed information about the workers and data from the Minnesota Cancer Surveillance System (MCSS).
Mesothelioma is a rare, fatal form of cancer seen almost exclusively in people who have been exposed to asbestos. MDH officials say it's not surprising to see additional reports of the illness among the miners, since it can take as long as 40 or 50 years to develop mesothelioma following exposure to asbestos. They expect to find additional cases as they complete work on designing the proposed study, and prepare to seek grant funding for the project.
MDH conducted an earlier study of mesothelioma in the miners after 17 of them were diagnosed with the rare illness. That study was completed in 2003. Thirty-five more cases were subsequently identified, bringing the total to 52, before MDH investigators began work on the new study and discovered the six additional cases.
The earlier study concluded that the 17 original mesothelioma cases could be accounted for by exposure to "commercial" asbestos, which is found in a variety of industrial settings, and is not unique to the mining industry.
The 2003 study was the first to ever conclusively document the occurrence of mesothelioma in Minnesota mine workers. However, the earlier study did not look at potential exposure of the workers to taconite dust.
The proposed new study will expand and build on the earlier study, but it will differ from the 2003 study in two important ways.
First, it will look at possible past exposure of workers to taconite dust, as well as potential exposure to commercial asbestos. Second, it will use a "case-control" strategy to compare workers who developed mesothelioma with those who did not, in an effort to determine what aspect of their jobs might have placed them at risk.
The relationship between respiratory disease and mining work has been a continuing concern in northeastern Minnesota, where unusually high rates of mesothelioma have been reported among male residents in the general population since the late 1980s. One hundred and forty-five cases of mesothelioma have been diagnosed in men who live in that part of the state since 1988