There are three principal variations of mesothelioma, based on where in the human body it develops. There are also three categories of malignant cells associated with the disease: cell type dictates the type of chemotherapy that is appropriate for treatment. In this section we'll review the basic medical facts that define a case of mesothelioma.
The only known cause for mesothelioma is the asbestos fiber. Asbestos is made up of these tough, flexible and tiny fibers that are invisible to the human eye. They impact humans when they make their way inside the body, which occurs when you either inhale them or ingest them inadvertently. They are small enough that you wouldn't know about the intake; they could be present in a cloud of dust caused by a deteriorating asbestos product. That cloud of dust could send fibers into your lungs, or allow them to float down on a sandwich at the work site.
Mesothelioma is a form of cancer that develops in the mesothelium, which is a membrane that lines many areas within the body. It wraps around the outer surfaces of both lungs as well as the outer surface of the heart. In addition, it lines the walls of both the chest cavity and the abdominal cavity. Asbestos fibers become embedded in the mesothelium, almost always in one of three areas: the portion that forms the outer lining of the lungs, the membrane wrapped around the heart, or the lining of the abdominal cavity. These three areas of the anatomy define the three types of cancerous mesothelioma. There is also a benign form of the disease, a rare occurrence that may be found in the mesothelium as well.
Pleural mesothelioma is cancer that develops in the outer lining of the lungs. Up to seventy percent of all mesothelioma cases are pleural; the term "mesothelioma cancer" is usually used in reference to this form of the disease. Often pleural mesothelioma is misdiagnosed because initial symptoms are usually a persistent cough, shortness of breath and tightness in the chest – symptoms that are found in much more common diseases such as pneumonia, emphysema and chronic bronchitis.
Pleural mesothelioma develops on one side of the chest, often leading to an accumulation of fluid outside the lungs called pleural effusion. This fluid caused by the thickening of the pleura causes tightness in the chest, reduced breathing capacity and chronic chest pain. Pleural mesothelioma will, in its advanced stages, often migrate into the lung itself which is why one of the surgical options for treating this form of the disease involves removal of the lung – the extrapleural pneumonectomy.
Twenty to thirty percent of all mesothelioma cases develop in the peritoneum, the membrane that lines the abdominal cavity. This version is called peritoneal mesothelioma; it seems to have a latency period of twenty to thirty years, shorter than the thirty to forty years attributed to pleural mesothelioma. No one is quite sure how asbestos fibers make their way to the abdominal cavity; one theory is that they are ingested and work their way through the wall of the digestive tract. Another is that they travel through the lymph system.
Excessive fluid accumulation can also be a symptom of this disease as the peritoneum thickens due to the development of inflamed, abnormal cells. The result is abdominal pain and often a distended abdomen as well. Gastrointestinal difficulties can be an unpleasant side effect of this form of mesothelioma; it advanced stages the malignant tissue may form on the lower intestine. As with pleural mesothelioma the symptoms of this disease mimic other more common maladies, which make a quick diagnosis unlikely. One review of the disease put the mean diagnosis time at 122 days after the patient was initially seen.
The pericardium is the membrane formed into a sac that surrounds the heart. Pericardial mesothelioma is a rare version of the disease, developing in perhaps five percent of all cases. The theory on development of this disease is that asbestos fibers are broken into pieces in the lungs, small enough that they can be carried through the bloodstream to the heart. There they lodge in the lining of the heart and develop mesothelioma in much the same fashion as asbestos fibers cause the more common pleural mesothelioma.
Once pericardial mesothelioma is active it can cause thickening of the pericardial membrane which can cause severe cardiovascular problems. Heart irregularities such as arrhythmia are common. Emergency surgery to relieve pressure on the heart may become necessary; fluid buildup in the area can exert some of that pressure along with the thickened mesothelium.
Types of Mesothelioma Cancer Cells
The cancer cells that develop as the result of asbestos fibers in the mesothelium are of two varieties, but manifest themselves in three different ways. Epithelioid cancer cells are the most common variety for mesothelioma cases of all types. The second and less common malignancy in mesothelioma is the sarcomatoid cell. This cell type is more often associated with peritoneal mesothelioma than with a pleural malignancy. The third category of cell configuration for mesothelioma is biphasic, a form of the disease that consists of both epithelioid and sarcomatoid cells.
The epithelial cell is by far the most common cause of mesothelioma, and is the cell type that is more likely to respond to treatment. Sarcomatoid cells do not respond well to treatment with the standard chemotherapy options for mesothelioma; patients who develop this type of the disease have an average survival period after diagnosis of less than six months.
Different cell types respond to different chemotherapy approaches. One cell might be best dealt with by attempting to block nourishment to the malignant area. Another might be more responsive to a type of enzyme associated with the immune system that will attack the malignant cell. Doctors are constantly experimenting with combinations of drugs to develop the most potent methods of stopping cancerous growth, and eliminating the existing cells.
- What is Malignant Mesothelioma, American Cancer Society, http://www.cancer.org/docroot/CRI/content/CRI_2_4_1X_What_is_malignant_mesothelioma_29.asp?sitearea=
- Extrapleural Pneumonectomy for Malignant…Mesothelioma Manual of Cardiothoracic Surgery, Sugarbaker et al, June 2005, http://mmcts.ctsnetjournals.org/cgi/content/full/2005/0628/mmcts.2004.000133
- Peritoneal Mesothelioma: a Review, Medscape General Medicine, Bridda et al, May 2010, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1994863/
- Lung Asbestos Fiber Content and Mesothelioma Cell Type, and Survival, Cancer, Leigh et al, June 1991, http://www.ncbi.nlm.nih.gov/pubmed/1646682