Mesothelioma and Lung Cancer
The rare
asbestos cancer known as
mesothelioma has many similarities to
lung cancer; it affects the same general area of the body and exhibits many of the same
symptoms. Yet there are some substantial differences—from the causes and development of the cancers, to the structure of the tumors, to their
treatment.
One of the reasons that these two diseases are often conflated is that exposure to the toxic material asbestos can cause both of them. Yet the two occur in different tissues of the body. Lung cancer affects the lung tissue itself, whereas mesothelioma attacks the
pleura, which is a thin membrane that both covers the lungs (and other organs) and lines the inside of the chest cavity. Mesothelioma may later metastasize to the lung tissue, but it always begins in the
mesothelium. Although
pleural mesothelioma is the most common form of the cancer, it can also strike the peritoneal or pericardial mesothelia, which surround and protect the stomach and the heart, respectively.
Asbestos exposure is the primary
cause of mesothelioma, although there are some other possible causes of the
disease—exposure to Thorotrast, a chemical once used in diagnostic X-rays, and to Simian virus 40, which contaminated several million polio vaccines. The relatively recent technology of carbon nanotubes has also fallen under scrutiny as being a possible source of
mesothelioma cancer, but none of these purported causes have been conclusively linked to the cancer to the same extent as asbestos.
On the other hand, lung cancer may be caused by a number of factors, or a combination. Smoking, secondhand smoking, a family history of the disease, and exposure to radon gas are all definitively linked to a higher incidence of lung cancer diagnoses.
Although patients
diagnosed with lung cancer may have large or multiple tumors, the tumors generally are individualized masses with clearly defined boundaries. This makes them easier for a surgeon to remove, thereby increasing the chances of actually curing the cancer. Mesothelioma, on the other hand, is characterized by diffuse malignancies; the “tumor” is not a contained mass but instead spreads across the surface of the mesothelium, rendering it extremely difficult to
surgically resect. In later stages, mesothelioma can actually encase the lung in a rind-like fashion. For the same reasons, lung cancer is more receptive to
chemotherapy and
radiation, whereas both of these therapies are usually unable to inhibit the growth of the diffuse
malignant tissues in mesothelioma.
Another significant difference between these two types of cancer is their rates of occurrence. Lung cancer is
diagnosed in approximately 200,000 new patients each year in the United States; mesothelioma cases number only about 3,000. The decline in cigarette smoking will undoubtedly cause lung cancer rates to fall, and mesothelioma rates are expected to peak in the coming decade, because the disease has such a long
latency period. Yet mesothelioma will always be a much rarer cancer than lung cancer.
Neither cancer has a particularly high survival rate, but the
prognosis for lung cancer is generally less grim than that for mesothelioma. Depending on the
stage, lung
cancer patients have a five-year survival rate between 15 and 75 percent, but fewer than 10 percent of
mesothelioma patients live two years or longer past
diagnosis. Typically, those who learn that they have
malignant pleural mesothelioma only live a few months.