Mesothelioma, a rare cancer of the lining of the lung, is caused by exposure to asbestos. Firefighters are at risk of asbestos exposure because of its frequent use in older structures and its ability to linger in the air even after a fire has been extinguished. Because of long dormancy periods, mesothelioma and other asbestos-related diseases can remain undetected for over a decade before the patient shows any signs of illness. An exposure of as little as one or two months can result in mesothelioma 30 or 40 years later.