Mesothelioma occurs when cells in the mesothelium become cancerous. The mesothelium is a thin membrane protecting the body’s vital organs. This cancer typically begins in the chest, heart or abdomen and can spread throughout the body. Mesothelioma is typically discovered in the advanced stages. The prognosis for an individual with mesothelioma is five to ten years. Asbestos exposure is the leading cause of developing mesothelioma.