Mesothelioma is a type of cancer that begins in the epithelial cells usually found on the outside of the lungs. Mesothelioma can begin anywhere where epithelial cells are normally located, although the most common site is the parietal pleura. Another name for mesothelioma is malignant mesothelioma. Mesothelioma is associated with asbestos exposure in most, but not all, cases. Many patients exposed to asbestos will also have areas where the pleura has become abnormally thickened. These areas are called pleural plaques and can usually be seen on imaging of the lungs (X-ray or CT scan). When examined under a microscope, pleural plaques consist of dense collagen layers…