The pleural lining is composed of two layers that provide protection and support for the lungs and other vital structures of the chest. It also produces a lubricating fluid for the cavity between the two layers to aid the expansion and contraction of the lungs as we breathe. The outer layer, the parietal pleura, lines the entire chest cavity. The inner layer, or visceral layer, covers the lungs.
It is not uncommon for mesothelioma to affect both layers of the pleura. Pleural mesothelioma generally develops in one layer of the pleura and rapidly invades nearby locations such as the diaphragm, chest wall or lung. If the cancer reaches the lymph nodes, it can metastasize, or spread, to distant locations in the body.