The relationship between lung cancer and malignant mesothelioma is often confused. By far the most common form of mesothelioma cancer is pleural mesothelioma, which develops in the layer of tissue that wraps around the outside of the lungs providing a protective layer for the lungs themselves. Because pleural mesothelioma develops in this lung lining it is often referred to as asbestos lung cancer. While mesothelioma is caused by asbestos, it is technically not lung cancer.
Primary Lung Cancer vs. Mesothelioma
Primary lung cancer is carcinoma that develops on the interior surface of the lung. It is most commonly associated with smoking as a principal cause. It is also far more common than mesothelioma; in 2006, for example, there were almost 200,000 diagnoses for primary lung cancer, while there were perhaps 3,000 new diagnoses of mesothelioma. There are occasions when primary lung cancer has developed as the result of asbestos exposure, but generally primary lung cancer develops from exposure to tobacco smoke.
Lung cancer is also a different type of cancer than mesothelioma. Primary lung cancer usually develops as a single tumor initially within one lung or the other. Mesothelioma is referred to as a “diffuse” type of cancer, meaning that it consists of a several small growths that are scattered across the surface of the pleura – the layer of tissue that wraps around the lungs, and that also lines the wall of the chest cavity.
Lung Cancer from Pleural Mesothelioma
However as pleural mesothelioma advances through the stages of cancer it can spread to both surfaces of the pleura, into the lymph system and ultimately may metastasize into cancer that forms in other locations. Pleural mesothelioma can metastasize into lung cancer; the fact that the pleura is located directly alongside the lungs means that malignant cells don’t have far to travel in order to reach the interior of the lung. Moreover, the asbestos fibers that cause mesothelioma usually arrive in the body through inhalation and initially lodge within the lung. When there are asbestos fibers that have made their way to the pleura there are almost always asbestos fibers within the lung as well, causing scarring of the tissue which results in asbestosis. These fibers may also cause the development of primary lung cancer.
On most occasions however mesothelioma develops independent of the presence of lung cancer. When pleural mesothelioma reaches stage four it may cause the development of lung cancer just as it causes the development of cancer in the lymph nodes. In those instances however the lung cancer is referred to as secondary to mesothelioma. It was triggered by the presence of malignancy in the pleura rather than as the first cancerous development within the body. It is known as secondary lung cancer rather than primary lung cancer.
Sources:
- Centers for Disease Control, http://www.cdc.gov/cancer/lung/statistics/
- Centers for Disease Control, http://www.cdc.gov/features/lungcancer/
- Agency for Toxic Substances & Disease Registry, http://www.atsdr.cdc.gov/tfacts61.html#bookmark01
- National Cancer Institute, http://www.cancer.gov/cancertopics/pdq/treatment/malignantmesothelioma/Patient/page2
