State health officials say they've identified another 21 cases of mesothelioma in former iron mine workers in northeastern Minnesota.
The new cases of the rare cancer were discovered in a group of 69,000 mine workers tracked by the Health Department and the University of Minnesota since the late 1990s. It brings the total number of cases in that group to 101.
"We have always expected to see additional cases as time went by," Health Commissioner Ed Ehlinger said in a statement. "We expect to see still more cases going forward."
While the number of mesothelioma cases in mine workers is high, health researchers aren't sure what's causing the spike in that disease or a number of other respiratory illnesses, such as cardiovascular disease and lung cancer.
For decades, some miners have wondered if microscopic needle-like fibers found in the dust of crushed taconite iron ore were lodging in workers' lungs and causing respiratory diseases. But a report issued by U of M researchers in December failed to establish a conclusive link.
The $4.9 million study, which began in 2008, found that many early workers in the taconite industry frequently handled asbestos, a known cause of mesothelioma, and researchers were unable to distinguish between exposure to those fibers from commercial asbestos and exposure to fibers in taconite dust.
The health department says the evidence suggests the problem is linked to exposure in the workplace rather than something found more broadly in the community. It notes that most of the mesothelioma cases have occurred in men, while women in the region have actually experienced lower than normal rates of the disease.