The majority of pleural mesothelioma cases involve the right lung. Medical researchers believe that this is because the right lung is usually larger than the left lung, and has more surface area for the fibers to penetrate. For similar mechanical reasons, most pleural mesotheliomas begin in the bottom lobe of the lung rather than the top lobe, because gravity pulls the fibers down once they have been inhaled.
At first the tumors are small – little more than bumps on the pleural tissue. However, the tumors grow together quickly and form a thin lining that adds to the thickness of the pleural sac. As time passes, the lining gets thicker and thicker as more cancerous cells develop, and the newly thickened lining begins pressing on the lungs, compressing them and compromising their ability to function. This is the point at which the patient generally begins to notice symptoms. At the same time as the pleural lining is thickening, the pleural tissue begins to secrete large quantities of fluid into the pleural area, adding still further to the pressure on the lungs. Breathing becomes painful and difficult.
The tumor now begins to form what appears to be a hard shell over the pleura, and starts expanding outward into the body.The tumor mass begins to shed cancer cells, which serve as tiny ambassadors of the disease to the rest of the body.The full-blown cancer begins to metastasize – and at this point it has become almost impossible to treat.