Mesothelioma is a disease in which malignant cancer cells are found in the mesothelium. The mesothelium is a protective sac that covers most of the bodies major organs. The mesothelium is made up of two layers of cells: One layer immediately surrounds the organ; The other layer forms a sac around it. The mesothelium produces a lubricating fluid that is released between these layers. The purpose of this lubricating fluid is to allow moving organs, such as the heart and lungs to glide against .