There are four primary types of mesothelioma based on the location where a tumor first develops: pleural (lungs), peritoneal (abdomen), pericardial (heart), and testicular. In addition, mesothelioma can be categorized based on cell type – epithelioid, sarcomatoid, or biphasic – and according to malignancy.
Mesothelioma Type by Location
The thin tissue lining where mesothelioma develops, known as the mesothelium, is located in certain areas of the body, such as the area of the chest surrounding the lungs and the abdominal cavity. The most common way to classify mesothelioma is to determine where in this mesothelial layer the disease originates.
Pleural mesothelioma develops in the lining of the lungs (known as the pleura). As the most common form of the disease, pleural mesothelioma accounts for approximately 80% of new cases.
Pleural mesothelioma is hard to diagnose. In the early stages of the disease, symptoms tend to be mild, while in later stages (stage 3 or stage 4) symptoms can worsen significantly. Unfortunately, since it is often diagnosed at a later stage, mesothelioma usually has a poor prognosis – most patients live less than 17 months from the time that their first symptoms appear.
Peritoneal mesothelioma originates in the lining of the abdomen. It often spreads to abdominal organs, including the liver, spleen, and bowel. Severe abdominal pain is the most common symptom, followed by discomfort caused by fluid buildup (abdominal effusion).
Although the prognosis for peritoneal mesothelioma is poor, it has improved somewhat in recent years, largely due to new treatments such as hyperthermic intraperitoneal chemotherapy (HIPEC). Outcomes vary from patient to patient, however, and survivorship typically depends on the individual’s situation and specific diagnostic factors.
Pericardial mesothelioma, which originates in the lining of the heart cavity (the pericardium), is uncommon – accounting for less than 1% of all mesothelioma cases. As this rare cancer progresses, the heart becomes unable to deliver oxygen to the body, causing further decline in health at an increasingly rapid rate.
The most common symptoms of pericardial mesothelioma mimic those of a heart attack, including pain in the chest and shortness of breath. In many cases, pericardial mesothelioma goes undiagnosed until an autopsy is performed.
Testicular mesothelioma is an extremely rare form of the disease, with fewer than 100 cases having been diagnosed around the world. Because there are so few incidents of this type of mesothelioma, little is understood about how it develops, and there is no standard course of treatment available.
Mesothelioma Cell Types
Currently, the only way to confirm a mesothelioma diagnosis is to determine its cell type. Usually, this is done by taking a tissue sample using a biopsy. The sample is then studied by a pathologist under a microscope (a process known as histology) to figure out which type of cells make up the tumor. Each cell type has multiple subtypes, as well.
Epithelioid mesothelioma is the most common cell type and accounts for approximately up to 75% of diagnosed cases. The cells are uniform in shape, with an elongated pattern that makes them easily distinguishable when viewed under high magnification. These types of cancer cells are adenocarcinomas, malignancies more commonly associated with lung cancer. Epithelioid mesothelioma has the best prognosis of any cell type.
Sarcomatoid mesothelioma is a less common cell type, accounting for between around 10% of mesothelioma cases. Sarcomatoid mesothelioma cells grow out of supportive structures, such as muscles and bones. They are long, spindle-shaped cells that are usually arranged in a seemingly haphazard way. Sarcomatoid mesothelioma has the worst prognosis of all three cell types, and it is usually the most difficult to treat.
Biphasic mesothelioma contains a mix of epithelial and sarcomatoid cell types, and it occurs in up to 40% of mesothelioma cases. While both types of cells exist in a biphasic tumor, in many cases the cells are differentiated, meaning that epithelioid cells are found in a separate area of the tumor from sarcomatoid cells. While biphasic mesothelioma has a better prognosis than sarcomatoid mesothelioma, it has a poorer prognosis than epithelioid mesothelioma.
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Types of Mesothelioma Tumors
Another way to categorize mesothelioma is based on whether the tumor is malignant or not. A malignant tumor indicates that it is harmful, and if left untreated, it will cause sickness and eventually death.
Most forms of mesothelioma are malignant, making the disease, as a whole, extremely deadly. Since mesothelioma has a long latency period, it can be extremely difficult to diagnose, making the malignancy that much more dangerous. However, even if a patient is diagnosed with malignant mesothelioma, there is still hope, especially if the disease is caught early. With the right treatment schedule, survivors can live for years after being diagnosed.
Benign mesothelioma is fairly rare and occurs in only a few limited cases. For example, well-differentiated papillary mesothelioma (WDPM) is commonly considered a benign form of mesothelioma. It is generally easier to treat than the malignant form of the cancer, and in most cases it can be treated successfully.Sources
Types of mesothelioma. Mesothelioma Research Foundation of America website.
Types of mesothelioma. Cancer Research UK website.
http://www.cancerhelp.org.uk/help/default.asp?page=4398. Updated November 10, 2015.