ST. PAUL, Minn. — Minnesota health officials and university researchers said Tuesday they've found 21 new cases of a rare form of lung cancer among a group of miners who they've been following since the late 1990s.

That brings the number of mesothelioma cases in the study group to 101. The state Department of Health and the University of Minnesota have been tracking 69,000 taconite workers to assess the risk from exposure to tiny mineral particles.

Dr. Ed Ehlinger, the state's health commissioner, told reporters Tuesday that researchers expected the additional mesothelioma cases, as the usually fatal disease can take decades to manifest.

"This is not new news. This is the continuation of what we normally would do," Ehlinger said.

The workers were employed in Minnesota's iron mining industry between the 1930s and 1982. Health officials say the 21 new cases and the previous ones occurred in individuals who worked in a number of places across the Iron Range and weren't limited to any one mining company or location.

The 21 new cases were all men, Ehlinger said, and all but three are now dead.

Exposure to asbestos is the biggest risk factor for mesothelioma, officials said. Commercial asbestos use has declined in the past decades, but Ehlinger said it's still a problem in some workplaces.