Types of Malignant Mesothelioma

Malignant mesothelioma is a rare form of cancer in which malignant cancer cells are found in the thin layer of tissue that lines the chest cavity and covers the lungs. This thin layer of tissue is called the pleura. Malignant mesothelioma is also a disease in which malignant cancer cells can be found in the thin layer of tissue that lines the abdomen and covers most of the organs in the abdomen. This thin layer of tissue is called the peritoneum.

Risk factors include working or living in a place where asbestos is inhaled or swallowed, living with a person who works near asbestos, and being exposed to a certain virus. The period between the time of exposure to asbestos and the onset of symptoms is about 20 to 50 years, which is why most cases are diagnosed later in life. Signs of malignant mesothelioma include trouble breathing, weight loss, lumps in the abdomen, pain under the rib cage, and pain or swelling in the abdomen. Roughly 3,000 people are diagnosed with malignant mesothelioma each year and the vast majority are men. Malignant mesothelioma is diagnosed through physical examination, chest x-ray, complete blood count or CBC, sedimentation rate, bronchoscopy, cytologic exam, or biopsy such as fine needle aspiration biopsy or FNA, thoracoscopy, laparotomy, or thoracotomy.

Malignant mesothelioma is divided into three types or “histological categories” including epithelioid mesothelioma, sarcomatoid mesothelioma, and biphasic mesothelioma. Malignant mesothelioma types are further divided into subtypes under each category. In many cases, malignant mesothelioma patients will have more than one type of cell.

Epithelioid mesothelioma accounts for roughly 50%-70% of all malignant mesothelioma cases. It is the most common cell type, exhibiting a uniform shape and tubular pattern with a unique cell nucleus. Epithelioid cells are shaped like cubes. Epithelioid mesothelioma occurs in the mesothelium, a protective layer of tissue called an epithelium that surrounds certain organs such as the lungs and gastrointestinal tract.  Symptoms of this type of malignant mesothelioma include chest pain, fluid build-up or pleural effusions, and respiratory difficulty. It is important to note that epithelioid mesothelioma is often confused with adenocarcinoma. It is recommended that individual’s diagnosed with adenocarcinoma seek a second opinion.

Sarcomatoid mesothelioma is also confused with other types of cancer due to the cells irregular oval shape. It is most often confused with sarcomatoid carcinoma, which is rare in the lungs. Sarcomatoid mesothelioma accounts for roughly 10%-15% of all mesothelioma cancer cells making it the least common form of malignant mesothelioma. The nucleus of sarcomatoid cells is tougher to detect under an electron microscope than the nuclei of epitheliold mesothelioma cells. Because sarcomatoid mesothelioma is often confused with sarcomatoid carcinoma as well as sarcoma, it is best to seek a second opinion – preferably from an oncologist specializing in mesothelioma.

Biphasic mesothelioma is fast becoming a major type of malignant mesothelioma. It is currently seen in approximately 46%-63% of all malignant mesothelioma cases. Biphasic mesothelioma is a combination of epithelioid and sarcomatoid mesothelioma cancer subtypes. It does not have a distinct cellular structure, but rather two very different mesothelioma cell types. This makes it easier to diagnose and less confusing than sarcomatoid or epithelioid mesothelioma. In biphasic mesothelioma, the tumor contains the two different subtypes in different parts of the tumor. In a nutshell, when a patient is diagnosed with biphasic mesothelioma, they are basically diagnosed with both epithelioid and sarcomatoid mesothelioma cancer.

Treatments for epithelioid mesothelioma, sarcomatoid mesothelioma, and biphasic mesothelioma are all the same. Treatments for malignant mesothelioma include two types: traditional mesothelioma treatments and new mesothelioma treatments. New malignant mesothelioma treatments include gene therapy, immunotherapy, intensity modulated radiation therapy or IMRT, photodynamic therapy or PDT and development of new chemotherapy agents. Traditional mesothelioma treatments include: surgery, chemotherapy, and radiation therapy or radiotherapy. In many cases a trimodality approach is employed, which means several treatments are combined for the very best outcomes, for a better chance at long-term survival, and/or a better quality of life. The type of treatment will also vary depending on the stage of the malignant mesothelioma. There are four stages.

Types of malignant mesothelioma surgery include pleurectomy/decortication, pneumonectomy, thoracentesis, and the most drastic type of surgery -- extrapleural pneumonectomy. Pleurectomy/decortication removes part of the infected lung and the surrounding chest lining; pneumonectomy involves total lung removal, and thoracentesis is a type of surgery that involves the draining of excess fluid from the lungs through a needle. This procedure aids in breathing and reduces stress and pressure on the lungs.  Pleurectomy/decortication and pneumonectomy are mostly performed to relieve pain and they rarely have an effect on the survival rate of patients.

Extrapleural pneumonectomy is typically performed in the earliest stages of malignant mesothelioma. It is a complicated procedure that involves the total removal of the linings that surround the lung, heart, and diaphragm. This will prevent the lining from being infected with mesothelioma. This procedure is performed on relatively healthy patients and in combination with chemotherapy and radiation. It typically takes a year to recover. While extrapleural pneumonectomy will extend life by several years, it is not a cure for any of the three types of malignant mesothelioma.

Radiation therapies for the three types of malignant mesothelioma include two main types: internal radiation therapy also known as brachytherapy and external radiation therapy. Radiation is used to kill cancer cells and shrink the tumor to a manageable size. It relieves pain and reduces symptoms such as shortness of breath. Radiation does not, however, come without consequences. In order to kill all of the cancerous cells, there can be significant damage to the patient.

Chemotherapy involves several types of anti-cancer drugs injected directly into the lungs or taken in pill form or intravenously. Chemotherapy drugs disrupt the growth of cancer cells in patients with malignant mesothelioma. Unfortunately, these drugs can damage normal healthy cells as well and can cause unpleasant side effects ranging from hair loss and nausea to anemia and hemorrhaging. Additionally, chemotherapy is not very effective in treating the three types of malignant mesothelioma.

'Types of Malignant Mesothelioma' Resources:
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  2. “Mesothelioma Questions and Answers” (online fact sheet) 5/13/2002
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  3. “Epithelioid, Sarcomatoid and Biphasic Mesothelioma Cancer Cell Types” (online article) 2005
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  4. “Types of Mesothelioma” (online article) 1/11/07
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  5. “Mesothelioma Treatment Options” (online article) 1/11/07
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