There are four primary types of malignant mesothelioma based on where the tumors initially develop following asbestos exposure: in the lining of the lungs (pleural), abdomen (peritoneal), heart (pericardial) or testicles (testicular).
Mesothelioma is further categorized by cell type, which can impact diagnosis, prognosis and available treatment options. The most common cell types for mesothelioma are sarcomatoid and epithelioid.
Mesothelioma Types by Location
Mesothelioma cancer forms after a person has been exposed to asbestos fibers. Years after initial exposure has occurred, abnormal cells begin to grow and multiply in the mesothelium, a thin layer of cells lining the outside of internal organs, including the lungs, heart, abdomen and testicles. The location of the tumors is the primary method for determining the type of mesothelioma.
Pleural mesothelioma forms in the lining of the lungs, known as the pleura, and is the most common form of the aggressive disease. Approximately 80% of all diagnosed cases of mesothelioma are pleural, and the disease is often not definitively diagnosed until it has progressed into its later stages.
Symptoms associated with pleural mesothelioma include shortness of breath, coughing, and fatigue, which are sometimes misattributed to other diseases, like lung cancer. Nonspecific symptoms, along with the long latency period after exposure to asbestos, complicate diagnosis. On average, pleural mesothelioma patients survive six to twelve months after diagnosis, with a one-year survival rate of about 73% and five-year survival rate of about 5%.
Peritoneal mesothelioma is the second-most common type of the cancer and is diagnosed in about 15-20% of all mesothelioma cases. Cancer cells grow in the lining of the abdominal cavity, known as the peritoneum, causing symptoms like abdominal pain and swelling, weight loss and fluid in the abdomen.
Though the general prognosis for peritoneal mesothelioma is poor, patients have a better life expectancy than other forms of the disease thanks to advancements in treatment, like surgery combined with hyperthermic intraperitoneal chemotherapy (HIPEC). Peritoneal mesothelioma patients have an average prognosis of six to twelve months, with a one-year survival rate of 92%. In addition, at least 50% of patients who undergo surgery combined with HIPEC will live five years or more.
Pericardial mesothelioma is a very rare form of the cancer and is diagnosed in only about 50 people in the United States each year, accounting for about 1% of the total number of cases. Mesothelioma tumors form in the lining of the heart sac, called the pericardium, causing symptoms like chest pain, fluid buildup and arrhythmia.
Because of the tumors’ proximity to the heart, patients may experience severe symptoms even at early stages. Due to its rarity, the general prognosis for pericardial mesothelioma is very poor. Patients survive six months on average, with a one-year survival rate of 51%. In most cases, pericardial mesothelioma patients only have palliative care options available to help alleviate symptoms.
Testicular mesothelioma is diagnosed in less than one percent of all cases and there are only about 100 diagnosed cases total. The cancer develops in the tunica vaginalis, the lining of the testicles, and typically presents symptoms like testicle pain, a mass on the testicle, and scrotal swelling caused by fluid buildup.
Patients with this type of mesothelioma have a better life expectancy than other forms, with an average prognosis of about two years. However, studies have shown that testicular mesothelioma does have a high rate of recurrence, including almost 93% of patients within five years of their initial diagnosis.
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Mesothelioma Cell Types
There are three main types of mesothelioma cells: epithelial, sarcomatoid, and biphasic. Depending on the type of cells found during lab tests, treatment options and life expectancy will change. Because epithelioid cells and sarcomatoid cells react differently to certain treatments, cell type is often taken into account when a mesothelioma specialist creates a treatment plan.
Epithelioid mesothelioma is the most common cell type and makes up about 75% of all mesothelioma cases. Epithelial cells are often associated with pleural mesothelioma, found in about half of all diagnoses. This cell type usually responds well to treatment and provides patients with a better prognosis than the other two cell types, with an average life expectancy of 12 to 24 months.
The most dangerous and difficult to treat of the three cell types, sarcomatoid mesothelioma accounts for about 10-20% of all diagnosed mesothelioma cases. These cells are associated with both pleural and peritoneal mesothelioma and, because of their aggressive growth, often leave patients with a very short prognosis of just six months.
When a patient has biphasic mesothelioma, both epithelial and sarcomatoid cells are present in the mesothelioma tumors. Because both types of cells are found, patients are often subject to varying prognoses, though it largely depends on which cells are more prevalent. Patients with more epithelial cells will likely have a better response to suggested treatments compared to those who have more sarcomatoid cells.
Mesothelioma cells may also sometimes be classified as rare subtypes of epithelial or sarcomatoid mesothelioma, including adenoid, cystic, well-differentiated papillary and small cell mesothelioma. Depending on what subtype is identified, it may limit what treatments are available and the prognosis a patient is given at diagnosis.
Also referred to as well-differentiated papillary mesothelioma, these cells are a rare subtype of epithelial mesothelioma. This form of the disease is most commonly diagnosed in women, and the exact cause is unclear. In most cases, papillary mesothelioma is benign and can be surgically removed, giving patients a favorable prognosis. In some studies, researchers have found patients survive for 20 years or longer.
Malignant vs. Benign Mesothelioma
Mesothelioma is categorized by the type of cells found in fluid or tissue samples taken from the body, and can be either benign or malignant.
Benign mesothelioma is a non-cancerous form of the disease. These tumors have a low rate of recurrence and can often be completely resected with surgery. Benign tumors are typically localized, slow growing and rarely metastasize to other parts of the body. In some cases, benign mesothelioma tumors may potentially become malignant, or cancerous.
Malignant mesothelioma makes up the vast majority of diagnosed cases. Malignant tumors often grow or spread quickly, which can limit viable treatment options. As such, patients with malignant mesothelioma live on average 12 to 21 months after diagnosis.
Mesothelioma Treatment by Type
Most mesothelioma patients will have several treatment options available to them depending on the type of disease. The three primary types of treatment available to patients include surgery, chemotherapy and radiation, though two or more treatments are often combined as part of a multimodal plan.
Patients who are diagnosed with early stage mesothelioma and are in generally good health may be candidates for potentially curative surgeries and more radical treatments. These can include extrapleural pneumonectomy (EPP) or pleurectomy/decortication (P/D) surgeries, along with new chemotherapy options like hyperthermic intraperitoneal chemotherapy (HIPEC) and Pressurized Intraperitoneal Aerosol Chemotherapy (PITAC). There are also immunotherapy and gene therapy options available through ongoing clinical trials.
As the disease progresses, options become more limited because surgical procedures become too dangerous to perform. Late stage mesothelioma often leaves patients with palliative options to reduce pain and increase quality of life.
Author: Linda Molinari
Editor in Chief, Mesothelioma Cancer AllianceRead about Linda
Reviewer: Annette Charlevois
Patient Support CoordinatorRead about Annette
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