What Are the Different Types of Mesothelioma?
Malignant mesothelioma is a type of cancer that originates in the lining of tissue called the mesothelium. The four main types of mesothelioma are based on the part of the body in which the tumors first grow:[1]
- Pleural mesothelioma. The tumors grow in the pleural tissue around the lungs.
- Peritoneal mesothelioma. Tumors develop in the peritoneal tissue of the abdominal cavity.
- Pericardial mesothelioma. This rare type grows in the pericardium, the tissue around the heart.
- Testicular mesothelioma. The rarest form of mesothelioma arises in the tissue surrounding the testicles.
Mesothelioma can also take the form of different cell types:
- Epithelial mesothelioma occurs strictly in the epithelial cells of the mesothelium.
- Sarcomatoid mesothelioma manifests as lengthened, spindle-shaped cells and can be difficult to distinguish from healthy tissue.
- Some mesotheliomas involve a combination of the two cell types, and these are referred to as biphasic.[2]
How Do the Mesothelioma Types Differ?
The types of mesothelioma differ in regard to which cell types they produce and affect, and which parts of the body they initially afflict. This can affect treatment.
In terms of cell types, epithelial mesothelioma is generally less difficult to treat than sarcomatoid or biphasic mesothelioma. The shape and location of the sarcomatoid cells make them difficult to differentiate from normal, healthy cells.
How Are They the Same?
All types of mesothelioma have a few things in common:
- They are aggressive cancers. The speed at which mesothelioma tends to grow and spread is very swift compared with other forms of cancer.[3]
- All types of mesothelioma affect the mesothelium, a thin layer of tissue found in different parts of the body.[4]
- Also, all mesotheliomas have long latency periods—a person who was exposed to asbestos may not experience symptoms and be diagnosed until long after he or she has reached retirement age, decades later.[5]
Pleural Mesothelioma
By far, the most common type of mesothelioma is pleural, accounting for about 75% of all diagnosed cases.[6] Pleural mesothelioma is cancer of the pleura, the part of the mesothelium that lines the lungs.
Because it occurs so close to the lungs, this type of mesothelioma is often mistaken for lung cancer. It is also likely the most common type because most mesothelioma cases are triggered by inhalation of asbestos fibers, which get lodged in the lungs and pleural tissue and cause damage.
Although it is the most common type of mesothelioma, pleural mesothelioma is still rare. Lung cancer, which can also be caused by asbestos exposure, is much more common. For these reasons, pleural mesothelioma is often misdiagnosed as a type of lung cancer but also often as pneumonia, bronchitis, and other common conditions.
Symptoms of pleural mesothelioma include chest pain. This is caused by the buildup of fluid in the pleural space, called pleural effusion.
Other symptoms reported include a chronic, sometimes painful cough, weight loss, fever, and shortness of breath.[7] Too often, these symptoms are mistaken for another health condition, and diagnoses of pleural mesothelioma come after the disease has progressed to a late stage.
Peritoneal Mesothelioma
The second most common type of mesothelioma affects the peritoneum. This is the part of the mesothelium that lines the abdominal space. Around 20% of mesothelioma cases are peritoneal.[8]
Inhalation of asbestos more often leads to pleural mesothelioma and other respiratory conditions, but the fibers can travel to the abdomen after inhalation. Accidental ingestion of asbestos may also trigger peritoneal mesothelioma.
Symptoms of peritoneal mesothelioma may include swelling and pain in the abdomen from fluid accumulation, bowel obstructions and constipation, anemia, weight loss, and fever. It may be misdiagnosed as a more common gastrointestinal condition, like irritable bowel syndrome.
Pericardial Mesothelioma
Very rare is pericardial mesothelioma, a cancer of the lining of the heart.[9] Only about 150 cases of a confirmed diagnosis of this type have ever been reported.
Its diagnosis is typically found in older patients and male patients. Symptoms of pericardial mesothelioma include chest pain, difficulty breathing, a chronic cough, an irregular heartbeat, fluid buildup around the heart, and a mass between the lungs. It may be misdiagnosed as a type of heart disease or heart failure.
Testicular Mesothelioma
The rarest of all types of mesothelioma affects the testicles in men. It is so rare that fewer than 100 cases have been reported. The official name of this type of cancer is tunica vaginalis testis mesothelioma, and it is the cancer of the mesothelium that lines the testes.
Most of the reported cases were in men over 50, but there have also been cases of men younger than 25 developing this type of cancer.[10]
The symptoms reported include a lump that can easily be mistaken for a hernia. With so few cases, though, there are not many other symptoms considered to be common. The prognosis for this type of mesothelioma is better than the others because surgical removal often cures it.
What Is the Difference Between Benign and Malignant Mesothelioma?
Nearly all mesothelioma cases are malignant, which means cancerous and with the potential to metastasize or spread to other locations. Benign tumors do not spread, and while they may cause complications, discomfort, or pain, they are not considered cancerous or life-threatening.
Benign mesothelioma is rare and, in fact, is not even always classified as mesothelioma.[11]
Misleadingly called benign mesothelioma, this type of tumor is more accurately called a solitary fibrous tumor of the pleura, peritoneum, or another part of the mesothelium.
It is called solitary because it usually grows as one lump, whereas malignant mesothelioma tumors grow as multiple smaller nodules. Treatment is straightforward, usually by surgical procedure, and the prognosis is generally good.
Different Cell Types in Mesothelioma
Each type of mesothelioma may affect different types of cells. Depending on which cell types are afflicted with cancer, mesothelioma is said to be epithelial, sarcomatoid, or biphasic.[12]
Each of these mesothelioma types comes with prognostic implications, with some more common than others and some more easily treated than others.
Epithelioid Cells
Pathologists can examine cells from a mesothelioma tumor biopsy and describe them as epithelioid, sarcomatoid, or biphasic. Epithelioid mesothelioma is the most common type, accounting for as much as 70% of cases.
These types of cells are easiest to treat, and this type of mesothelioma has the highest survival rates. This is because the epithelioid cells, as compared to others, adhere more closely to each other. They are less likely to spread from a tumor and do so more slowly. There are several subtypes of epithelioid cancer cells that can be used to further classify a diagnosis.
Sarcomatoid Cells
Sarcomatoid mesothelioma cells are much less common than epithelioid cells. Only about 10-20% of diagnosed cases of pleural mesothelioma and 4% of peritoneal mesothelioma are of this type.
Sarcomatoid cells are much more aggressive, detach from each other more easily, are more likely to spread, and spread faster than malignant epithelioid cells. Treating sarcomatoid mesothelioma is more difficult due to the aggressive tendency of the cells to metastasize. The prognosis is much less positive for most patients with this diagnosis.
Biphasic Cells
When a pathologist finds both types of cells, epithelioid and sarcomatoid, in a cell sample from a mesothelioma tumor, the cancer is classified as biphasic. This accounts for about 20-30% of cases of mesothelioma. The amount of each type of cell varies by patient. This means that prognosis and survival rates are varied. The more epithelioid cells there are, the better the prognosis.
Types of Mesothelioma by Stage
Mesothelioma also differs by stage. Oncologists stage cancer based on several factors, giving a patient a diagnosis of stage 1, 2, 3, or 4.
- Stage 1 Mesothelioma. This is a rare type of mesothelioma diagnosis. It’s a difficult cancer to diagnose when the symptoms are still mild or similar to those of other illnesses. In stage 1, the cancer remains localized to the mesothelium.
- Stage 2 Mesothelioma. In stage 2, the cancer has spread throughout the mesothelial tissue. In pleural mesothelioma, it is likely still on one side of the pleura. There may also be cancer in the lung or diaphragm on the same side of the chest.
- Stage 3 Mesothelioma. Stage 3 mesothelioma is characterized by the spread of tumors throughout the mesothelium, to both sides of the chest, and potentially to nearby lymph nodes.
- Stage 4 Mesothelioma. Stage 4 mesothelioma is usually metastatic. The tumors have spread extensively to the lymph nodes, to other parts of the body, or both.
How Do Doctors Treat Different Types of Mesothelioma?
Typical mesothelioma treatment methods include surgery, radiation therapy, chemotherapy, and novel therapies such as those explored in clinical trials.[13] Different types of mesothelioma respond better to different types of treatment. In many cases, a multi-therapy approach using two or three types of treatment is the best option.
Treatment by Cell Type
- Epithelial mesothelioma can often be treated with surgery. Often, surgery is combined with chemotherapy or radiation treatment—either before, during, or after surgery—to eliminate cancerous cells that the surgery may not have completely eradicated. Epithelial mesothelioma is considered the most treatable form of this cancer, with the most options open for different treatment methods.
- Sarcomatoid mesothelioma can be extremely difficult to treat using surgical means, as the cells become very stiff and rigid and tend to embed themselves firmly into a patient’s internal organs. For this reason, chemotherapy and radiation treatments are the most popular options for this form of cancer. In many cases, sarcomatoid mesothelioma treatments are palliative rather than curative due to the aggressive spread involved in this cancer type.
- Biphasic mesothelioma can be treated with surgery, chemotherapy, radiation, or a multimodal approach combining various treatment types. For example, epithelial cancer may be removed surgically, while sarcomatoid cancer may be targeted with chemotherapy and radiation treatment. Treatments for biphasic mesothelioma may be both curative and palliative, depending on the extent of growth and spread of the cancer. This form of mesothelioma has a better prognosis than the sarcomatoid form but is not as promising a prognosis as most epithelioid mesothelioma diagnoses.
Treatment by Location
- Pleural mesothelioma treatment is typically agressive and multimodal. To slow or stop the spread of disease, doctors may use surgery, chemotherapy, radiation, and other treatments like immunotherapy.
- Peritoneal mesothelioma especially benefits from cytoreductive surgery, a procedure to remove as much of the cancerous tissue from the abdomen as possible. This is usually followed by the circulation of chemotherapy drugs throughout the abdominal cavity.
- Pericardial mesothelioma is often treated with a pericardiectomy, a surgical procedure to remove the lining around the heart. Patients may also receive chemotherapy.
- Testicular mesothelioma is the most treatable type of mesothelioma. The most common treatment is to remove the testicle. This may or may not be followed by chemotherapy and radiation.
Treatment by Stage
- Treating stage 1 mesothelioma rarely occurs, only because most patients don’t get diagnosed so early. However, patients in this stage benefit most from aggressive treatments, including extensive surgery, chemotherapy, and radiation.
- Treatment for stage 2 mesothelioma is similar and usually involves an aggressive surgical procedure to remove tumors and follow-up therapies to eliminate any remaining cancer cells.
- Stage 3 mesothelioma is considered late-stage, with limited treatment options. Surgery may or may not be an option, depending on the patient. Chemotherapy is the most common treatment.
- Once a patient has reached stage 4 mesothelioma, they are not likely to be eligible for surgery. Most patients receive chemotherapy along with palliative treatments.
Understanding mesothelioma types is important for diagnosis and treatment, but also for the patient to know what to expect. If you have questions about your diagnosis, the type of mesothelioma, or any concerns about mistakes or misdiagnosis, don’t hesitate to speak up, ask questions, or get a second opinion.
