The most common form of the disease, pleural mesothelioma develops in the the lining of the lungs, also known as the pleura.

The pleura is made up of two layers that protect the lungs and chest cavity. The outer layer lines the diaphragm and chest cavity, while the inner layer covers the lungs. In most cases, pleural mesothelioma occurs in only one layer, but can spread to the other.

Like other forms of mesothelioma, pleural mesothelioma is caused by the inhalation of asbestos fibers which become trapped in the lungs. These fibers become embedded in the lining of the lungs and cannot be extracted unless the fibers attach to mucous and are coughed up. Eventually, the chronic inflammation can lead to the growth of cancerous tumors.

Pleural mesothelioma usually appears as several tumors affecting both the outer and inner layer of the pleura. Usually, the outer layer has more involvement than the inner layer. In addition, the right lung is more likely to be affected, due to its larger pleural surface area. The lower part of the lungs also typically show more tumor growth than the upper region. Researchers believe this occurs because of the gravitational effect on asbestos fibers in the lungs.

As the tumors grow, a complete obliteration of the lung cavity can occur. The tumors can also spread to nearby organs, such as the heart or abdomen. In some cases, mesothelioma can also invade the circulatory system and the lymph nodes. 

Symptoms of pleural mesothelioma typically appear 20 to 50 years after asbestos exposure. The most common symptoms of pleural mesothelioma include:

• Chest pain
• Coughing
• Unexplained weight loss
• Shortness of breath