Mesothelioma and Lung Cancer
Pleural mesothelioma is the most common form of mesothelioma, and as such, is often considered or spoken of as a form of lung cancer, but this is incorrect. Mesothelioma and lung cancer are completely different diseases, with different origin sites, tumor structure and treatability.
Mesothelioma is a cancer that affects the mesothelium, which are the serous membranes that protect and support different organs in the body by secreting fluid that reduces friction and eases movement of those organs within their respective body cavities. Pleural mesothelioma affects the pleural surfaces in the chest cavity. The parietal pleura lines the inner chest wall and the visceral pleura encases the lungs. The fluids secreted by each pleura enable the lungs to move easily when breathing. The tumors can spread to the lungs and invade its inner tissues, but the origin site of the cancer remains the pleura.
The other major form, peritoneal mesothelioma, which affects mesothelial tissue in the peritoneum, can also spread to the lungs, but its origin site remains either the parietal or visceral peritoneum.
Cancer guidelines teach that a tumor which invades another surface is still a form of the original cancer and generally retains its overall structure and behavior. It is because of these guidelines that we speak of mesothelioma as distinct from lung cancer.
Differences Between Mesothelioma and Lung Cancer
Mesothelioma is a diffuse malignancy. It invades a tissue area as a large number of interlocked tumors and the boundaries between malignant tissue and healthy tissue are blurred and, eventually, dissolved. This is the primary reason that mesothelioma remains so difficult to treat. The large extent of malignant tissue makes complete surgical resection very difficult. Chemotherapy is generally unable to inhibit the growth of so many masses, nor is radiation effective over such large areas. In its late stages, the cancer engulfs the invaded tissues, wrapping completely around it and restricting its ability to move.
Lung cancer works differently. It arises within the lungs themselves and is characterized by individualized tumor masses. Even for people with multiple masses, the tumors generally possess clear boundaries. The tumors can grow quite large and in its late stages and most aggressive forms, lung cancer is just as deadly as mesothelioma. However, it is much more amenable to treatment. Because of the individualized natures of its tumors, it is possible to completely remove all visible malignant tissue. Chemotherapy and radiation are more effective treatment modalities as well. None of this is to say that lung cancer is not a serious diagnosis, because it is a deadly serious disease. It is simply to draw a clear difference between the two cancers.
There are other differences between lung cancer and mesothelioma as well. While asbestos exposure is a causative factor for both disorders, it is the only known cause of mesothelioma while lung cancer can be caused by other agents—including cigarette smoking.
Another difference between the two involves the incidence rates between the diseases. Mesothelioma is a rare disorder, affecting about three thousand people per year, while lung cancer has a diagnostic rate 65 times greater with nearly 200,000 yearly diagnoses. As people stop smoking, lung cancer incidence is expected to drop but oncologists still expect decades of tobacco-related lung cancers.
Mesothelioma and lung cancer are two very different diseases. While the most common form of mesothelioma begins in tissue very close to the lung, the very real differences in tumor structure and malignant behavior clearly identify the individual differences between these forms of cancer.