Mesothelioma

What is Mesothelioma?

Mesothelioma is a rare and aggressive form of cancer almost exclusively caused by asbestos exposure. Mesothelioma is specifically a cancer of the mesothelium – a membrane that forms the lining of multiple body cavities, most notably the pleural cavity, the abdominal cavity and the pericardium. Mesothelioma most often affects the pleural lining, as this lining surrounds the lungs. When asbestos fibres are inhaled into the lungs, they embed in the lung lining causing the inflammation of the pleura. In other cases, asbestos can cause inflammation in the abdominal or cardiac mesothelial membranes. This inflammation irritates the mesothelial cells, causing genetic mutations that develop into tumors over time1.

Mesothelioma is one of the most aggressive forms of cancer. This is, in part, due to the location of tumour development. The mesothelium is located in the chest and abdominal cavities, which is close to many of the body’s vital organs. Therefore, when it metastasizes, it may affect these organs quickly.

There are three different forms of mesothelioma, depending on the cell type of the cancer. First, and most commonly, is epithelial mesothelioma. Epithelial mesothelioma accounts for 50-70% of all mesothelioma cases2. It is defined by affecting only epithelial cells, which are of uniform size and shape, and resemble normal epithelial cells. As it is the most common form of mesothelioma, it is the most widely studied. The next type of mesothelioma is sarcomatoid mesothelioma. It is defined by having random and irregular cell shapes, typically elongated and without a nucleus. This type occurs in approximately 10 to 15% of all mesothelioma cases2.This type of mesothelioma is often more difficult to diagnose, as it is more difficult to distinguish from healthy tissue and more difficult to biopsy. The last type of mesothelioma is biphasic, and accounts for 20-35% of mesothelioma cases2. This type contains a mix of epithelial and sarcomatoid cells. Characteristics of this type depend on the ratio of epithelial to sarcomatoid cells, with a larger proportion of sarcomatiod cells providing a less favourable prognosis. This cell type is more common among pleural patients.

Symptoms of Mesothelioma

Mesothelioma is a very difficult cancer to diagnose, which makes it very hard to catch at an early stage. What makes it even more difficult to diagnose is the latency time between exposure to the main risk factor, asbestos, and the onset of cancer. Since the latency period is typically between 20 to 50 years3, it can be very hard to predict if and when mesothelioma might develop. Furthermore, the long latency period may mean individuals may fail to make the connection between symptoms and their early exposure to asbestos.

Symptoms of mesothelioma include persistent cough, shortness of breath, and pneumonia-like symptoms4.

How is Mesothelioma Diagnosed?

To diagnose mesothelioma, a doctor will begin by taking the patients’ medical history to establish risk factors for mesothelioma. If there are many risk factors present, the doctor will then perform a physical exam to look for fluid in the lungs or abdomen. They may then order medical imaging to determine whether any irregularities are present and/or order a blood test to look for cancer related proteins. Finally, to confirm the diagnosis, the doctor will order a biopsy of the affected area. The biopsy can be done using a needle, endoscope or can be performed surgically.

A needle biopsy may be useful as a first attempt at a biopsy, as it is less invasive than other methods. A needle is used to pass between the ribs and the pleura, and a small sample of the tumour is removed. The difficulty in using this method for mesothelioma is that it may not remove a sample large enough for diagnosis. In this case a more invasive biopsy is needed.

An endoscopic biopsy uses an endoscope, a thin tube with a light and camera at the end, to look for the tumour(s). An endoscope can be used in the thorax (chest), abdomen or mediastinum, the area between the lungs. Endoscopic procedures are performed under general anaesthetic, when a surgeon makes a small incision in the desired cavity to guide the endoscope. The surgeon will look for the tumour with the endoscope and will remove small pieces of tissue for microscopic examination.

If the previous methods of biopsy prove ineffective, a doctor may then suggest an open surgical biopsy, which allows the surgeon to remove a larger sample of the tumour.

What are the Treatment Options?

Unfortunately, there is currently no known cure for mesothelioma, and remission from mesothelioma is unlikely due to the nature of the cancer. However, life expectancy for patients with mesothelioma has increased in recent years as treatment options have improved5. Treatment is dependent on the type and stage of the cancer, and can include surgery and radiation as well as experimental cancer treatments. The course of action for managing mesothelioma depends on the specific case characteristics. Currently in Canada, the 5-year survival rate for mesothelioma is 7%6. However, it is important to note that survival rate can increase or decrease depending on the stage of the cancer, location, type of cancer and age.

What is the Prognosis?

The prognosis of a patient with mesothelioma depends on specific characteristics of the individual and of the cancer. Currently in Canada, the 5-year survival rate for mesothelioma is 7%6. However, it is important to note that survival rate can increase or decrease depending on the stage of the cancer, location, type of cancer and age.

In general, the lower the stage of the cancer, the better the prognosis. For example, in stage I, the cancer is localized and any additional tumours are close to the originating tumour, so surgery may be an effective strategy for removing the cancer.

The location of the cancer also affects survival, with those diagnosed with pleural mesothelioma having a better prognosis than those with peritoneal mesothelioma or pericardial mesothelioma.

As previously mentioned, mesothelioma can occur in one of three types: epithelial, sarcomatoid or a mix of the two. Those with epithelial mesothelioma have a better prognosis.

Finally, age can play a part in prognosis, as younger and stronger patients typically have better general health than older patients.

If you are interested in learning more about clinical trials currently being offered for mesothelioma patients in Canada, visit http://www.canadiancancertrials.ca/.

 

References

1. Park, S., Schalling, M., Bernard, A., Maheswaran, S., Shipley, G.C., Roberts, D., Fletcher, J., Shipman, R., Rheinwald, J., Demetri, G., Minden, M., Housman, D.E., and Haber, D.A. (1993) The Wilms tumour gene WT1 is expressed in murine mesoderm-derived tissues and mutated in human mesothelioma. Nature Genetics 4: 415-420.

2. Mesothelioma Cancer Alliance (2015) Mesothelioma Types. Retrieved July 2015 from http://www.mesothelioma.com/mesothelioma/types/

3. Lanphear, B.P., and Buncher, C.R. (1992) Latent period for malignant mesothelioma of occupational origin. Journal of Occupational Medicine 37: 718-721.

4. Mesothelioma Cancer Alliance (2015) Symptoms of mesothelioma. Retrieved July 2015 from http://www.mesothelioma.com/mesothelioma/symptoms/

5. Mesothelioma Cancer Alliance (2015) Mesothelioma Life Expectancy. Retrieved July 2015 from http://www.mesothelioma.com/mesothelioma/prognosis/life-expectancy.htm

6. Canadian Cancer Society (2015) Survival statistics for mesothelioma. Retrieved July 2015 from http://www.cancer.ca/en/cancer-information/cancer-type/mesothelioma/prognosis-and-survival/survival-statistics/?region=on