Types of Mesothelioma: Comparison and Contrast

Malignant mesothelioma is an extremely uncommon and aggressive type of cancer. It is generally associated with exposure to carcinogenic fibrous minerals such as asbestos over the long term. Mesothelioma is unique in that is has an unusually long latency period, so the time from first exposure to a carcinogen to becoming symptomatic may span decades, a half a century, or longer.

What Types of Mesothelioma Are There?

Malignant mesothelioma is the name of a specific type of cancer which may occur in the linings of the lungs (pleural mesothelioma), abdominal cavity (peritoneal mesothelioma), heart (pericardial mesothelioma) or testis (paratesticular mesothelioma). Mesothelioma cancer may also produce different cell types: epithelial mesothelioma occurs strictly in the epithelial cells of the mesothelium, whereas sarcomatoid mesothelioma manifests in lengthened, spindle-shaped cells and can be difficult to tell apart from healthy tissue and thus. Some mesotheliomas involve a combination of the two cell types, and these are called biphasic.

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. Pleural and peritoneal mesothelioma may be more easy to treat than pericardial and paratesticular mesothelioma. Also, epithelial mesothelioma is generally regarded as being less difficult to treat than sarcomatoid or biphasic mesothelioma, as the shape and location of the sarcomatoid cells makes them difficult to differentiate from normal, healthy cells.

How Are They the Same?

All types of mesothelioma have one thing 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. Also, all mesotheliomas share in the long period of dormancy—a person who was exposed to asbestos or another fibrous carcinogen as a young adult may not experience symptoms and be diagnosed until long after he or she has reached retirement age.

Pleural Mesothelioma

By far the most common type of mesothelioma is pleural, accounting for about 75 percent of all diagnosed cases of this cancer. Pleural mesothelioma is cancer of the pleura, the part of the mesothelium that lines the lungs. For this reason, this type of cancer is often mistaken for lung cancer. It is also likely the most common type because most cases of mesothelioma is triggered by inhalation of asbestos fibers, which get lodged in the lungs and cause damage.

Although it is the most common type of mesothelioma, pleural mesothelioma is 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 and fever, and shortness of breath. 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 the part of the mesothelium that lines the abdominal space. Between ten and 20 percent of mesothelioma cases are peritoneal. Inhalation of asbestos more often leads to pleural mesothelioma and other respiratory conditions, but the fibers can travel to the abdomen after inhalation. Peritoneal mesothelioma may also be triggered by accidental ingestion of asbestos.

Peritoneal mesothelioma may trigger a number of symptoms: abdominal pain from the buildup of fluid, abdominal swelling, the presence of an abdominal mass, weight loss, bowel obstructions, anemia, and fever. This type of mesothelioma may be misdiagnosed as irritable bowel syndrome or other more common abdominal and gastrointestinal conditions.

Pericardial Mesothelioma

Pericardial mesothelioma is very rare and is a cancer of the lining of the heart. Only about 150 cases of confirmed diagnosis of this type have ever been reported. It seems to be more common in older patients and in male patients. Symptoms of pericardial mesothelioma include chest pains, 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 few reported cases were in men over 50, but there has been a significant number of cases of men younger than 25 developing this type of mesothelioma.

Symptoms for this type of mesothelioma are not well-reported because it is so rare, but most men diagnosed start out with what seems to be a hernia. A fluid-filled sac on a testicle may also be a sign of the cancer. Treatment for this mesothelioma is usually surgical and the prognosis for patients is better than for pleural mesothelioma.

Benign vs. Malignant

Nearly all cases of mesothelioma 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, are not considered cancerous or life-threatening. Benign mesothelioma is rare, and in fact is not even always classified as mesothelioma.

Misleadingly called benign mesothelioma, this type of tumor is more accurately called a solitary fibrous tumor of the pleura, peritoneum, or other part of the mesothelium. It is called solitary because it usually grows as one lump, whereas malignant mesothelioma tumors grow as multiple smaller nodules. A solitary fibrous tumor is not typically linked to asbestos exposure, and it can usually be removed surgically and not cause any more problems for a patient.

Treating benign mesothelioma is much more straightforward than malignant mesothelioma. Most people have an excellent prognosis and can be cured by simply having the tumor surgically removed. Even when the tumor comes back years later, it just needs to be removed again. Only in extremely rare cases does a benign mesothelioma tumor become malignant.

How Mesothelioma Affects Different Cell Types

Each type of mesothelioma may affect different types of cells. Depending on which cell types are afflicted with the cancer, the mesothelioma is said to be epithelial, sarcomatoid, or biphasic. Each of these mesothelioma types come with prognostic implications, with some types being more common than others and some types being more easily treated than others.

Epithelioid Cells

All four types of malignant mesothelioma can further be classified by cell type. Pathologists can look at cells from a mesothelioma tumor under the microscope and describe them as either epithelioid, sarcomatoid, or biphasic. Epithelioid mesothelioma is the most common type, accounting for as much as 70 percent 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 mesothelioma.

Sarcomatoid Cells

Sarcomatoid mesothelioma cells are much less common than epithelioid cells. Only about ten to 20 percent of diagnosed cases of pleural mesothelioma and four percent of peritoneal mesothelioma are of this type. This is good news for most patients because these cells are much more aggressive, more likely to spread, and spread faster than malignant epithelioid cells.

Treating this type of mesothelioma is more difficult due to the aggressive tendency of the cells to metastasize, and the prognosis is much less positive for most patients with this diagnosis. Pathologists can usually easily see the difference between the two types of cells under the microscope. Sarcomatoid cells have a distinctive, spindle shape and gather together in fibrous bundles.

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 to 30 percent 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.

Mesothelioma is a complex and aggressive type of cancer. Poor survival rates are compounded by how difficult it is to diagnose this type of cancer. Misdiagnoses and late diagnoses too often lead to late stage diagnoses that are difficult to treat successfully. Understanding the different types of mesothelioma is important in making a more accurate diagnosis, being able to stage the cancer correctly, and being able to plan the best course of treatment. If you suspect you may have one of these types of mesothelioma, even one of the very rare types, don’t hesitate to talk to your doctor about your concerns and your symptoms. Getting a diagnosis early is the best chance you have.

Treating Different Types of Malignant Mesothelioma

The typical treatment methods for mesothelioma include surgery, radiation therapy, chemotherapy and novel therapies such as those explored in clinical trials. Different types of mesothelioma respond better to different types of treatment.

Epithelial mesothelioma can often be treated with surgery, as the cancerous cells are easier to spot with the naked eye in order for a surgeon to remove them from the body. Often, surgery is combined with chemotherapy or radiation treatment—either before, during or after surgery—in an effort 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. With peritoneal mesothelioma, for example, the sarcomatoid cells may cling to the patient’s intestines, making surgical removal very challenging. 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, the epithelial cancer may be removed surgically while the 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 not as promising a prognosis as most epithelioid mesothelioma diagnoses.