Written By: Devin Golden
Sarcomatoid Mesothelioma
Sarcomatoid mesothelioma is the rarest cell type, accounting for between 10% and 20% of cases.
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Important Facts About Sarcomatoid Mesothelioma
- Sarcomatoid mesothelioma is a rare diagnosis and has the poorest life expectancy.
- Sarcomatoid cells form from epithelioid cells that transition after asbestos exposure.
- The nature of how sarcomatoid cells grow and spread makes sarcomatoid mesothelioma tough to treat.
What Is Sarcomatoid Mesothelioma?
Sarcomatoid Cell Type
Sarcomatoid mesothelioma is a cellular type of mesothelioma. It’s also called “fibrous mesothelioma” due to its appearance.
This form of mesothelioma metastasizes fast, meaning tumors spread quickly to other areas of the body. Sarcomatoid mesothelioma is the least treatable cell type, though new treatments are leading to longer life expectancies.
According to a report in Modern Pathology, sarcomatoid mesothelioma forms far more often in the pleura than it does in the peritoneum. A study showed that 98% of sarcomatoid cases are pleural mesothelioma.
Characteristics of Sarcomatoid Mesothelioma Cells
Cell Description
Sarcomatoid cells are spindle-shaped, meaning they look long and narrow. They have enlarged, elongated nuclei. These cells can have more than one nucleus and are hard to distinguish from healthy tissue.
Cell Behavior
Sarcomatoid cells do not form in regular patterns like epithelioid cells do. Instead, they proliferate through soft tissue and are difficult to find and remove.
How Sarcomatoid Mesothelioma Forms
The human body is comprised of four types of cells, one being epithelial cells. The epithelial cells along the linings of the lung cavity, abdominal cavity and heart are called mesothelial cells.
When asbestos fibers reach these linings, they can lodge into and irritate mesothelial cells. This is how mesothelioma forms.
Many of the diseased cells remain epithelial cells, which is why epithelioid mesothelioma is the most common cell type. However, some epithelial cells transform into sarcomatoid cells when they become cancerous.
This change occurs due to the epithelial-to-mesenchymal transition (EMT). This process involves epithelial cells changing into mesenchymal cells, which are part of the body’s connective tissue (such as bones and cartilage).
Cancerous connective tissue cells are called sarcomas, which is the origin of sarcomatoid mesothelioma. Epithelioid cells can be present in sarcomatoid mesothelioma but comprise less than 10% of the cells. If the amount is 10% or higher, then the cancer is considered biphasic mesothelioma.
Epithelial cells line the thin membrane just outside of the lung cavity, abdominal cavity and heart.
Epithelial cells can transform into sarcomatoid cells when they become cancerous. This change is called the epithelial-to-mesenchymal transition (EMT).
Mesenchymal cells are usually part of the body’s connective tissue (such as bones and cartilage). When they become cancerous, they are called "sarcomas."
Sarcomatoid Mesothelioma Symptoms
Symptoms of mesothelioma can mimic those caused by other illnesses. This is one of the reasons why early detection is so difficult.
Symptoms of sarcomatoid pleural mesothelioma include:
- Chest or lower back pain
- Shortness of breath
- Pleural effusion (fluid buildup)
Symptoms of sarcomatoid peritoneal mesothelioma include:
- Abdominal pain
- Ascites (fluid buildup)
- Anorexia and nausea
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Diagnosis
Sarcomatoid mesothelioma is difficult to identify because of how infrequently patients develop this cell type. Doctors are not familiar with sarcomatoid mesothelioma and cells look similar to benign tissue.
In order for doctors to get a definitive diagnosis, they will perform a fluid extraction or tissue biopsy.
This kind of mesothelioma is difficult to identify and the concentration of malignant cells in the biopsy might be too low to detect. Therefore, the initial microscopic analysis might be inconclusive.
If the biopsy is adequate, pathologists will use immunohistochemistry to accurately define the cell type. This process involves tissue staining to analyze proteins in the cell samples. Proteins are markers to distinguish each cell type. Doing so gives pathologists a way to diagnose patients with this rare form of mesothelioma.
IImmunohistochemical markers (proteins) for diagnosing sarcomatoid mesothelioma include:
- Podoplanin (D2-40)
- Pancytokeratin
- Calretinin
- GLUT1
Second Opinions
Patients diagnosed with mesothelioma, particularly with less common cell types like sarcomatoid, should seek a second opinion. Having a mesothelioma specialist analyze diagnostic tests can make a difference when planning treatment.
The long latency period of mesothelioma, along with its aggressive behavior once the tumors form, can lead to a misdiagnosis. Many physicians are not qualified to identify mesothelioma and will attribute symptoms and test results to other illnesses.
Treatment
If a sarcomatoid mesothelioma patient can have surgery, their operation depends on their type of mesothelioma. Pleural mesothelioma surgeries include extrapleural pneumonectomy (which removes the affected lung) and pleurectomy with decortication (which spares the nearby lung).
Peritoneal mesothelioma surgery is cytoreduction with heated intraperitoneal chemotherapy.
Surgery
If a sarcomatoid mesothelioma patient can have surgery, the operation they’ll have depends on their type of mesothelioma and how developed the disease is. Pleural mesothelioma surgeries include extrapleural pneumonectomy (which removes the affected lung) and pleurectomy with decortication (which spares the lungs).
Peritoneal mesothelioma surgery is primarily cytoreduction with heated intraperitoneal chemotherapy.
Chemotherapy, Radiation and Emerging Methods
With studies and clinical trials currently underway, researchers hope to develop improved treatment methods through immunotherapy, virotherapy, gene therapy and other novel treatments. These forms of care could increase survival rates in the future.
According to a published report in the Journal of Thoracic Oncology, two medical groups state that a sarcomatoid mesothelioma diagnosis should not exclude a patient from chemotherapy or clinical trials.
The United States Food and Drug Administration has approved two chemotherapy drugs — pemetrexed and cisplatin — for mesothelioma. The FDA also approved two immunotherapy drugs (Opdivo and Yervoy) for unresectable mesothelioma cases.
Radiation is another treatment option, although it’s often used as a second-line treatment either before or after surgery.
Subtypes of Sarcomatoid Mesothelioma
There are three subtypes of sarcomatoid mesothelioma. The subtype of the cancer can affect treatment. Certain subtypes are less responsive to traditional treatments and add a layer of complexity to the diagnostic process.
- Transitional mesothelioma
- Lymphohistiocytoid mesothelioma
- Desmoplastic mesothelioma
Prognosis
The prognosis for sarcomatoid mesothelioma is not as hopeful as the other two cell types. According to a 2018 study published in Clinical Lung Cancer, the median survival rate for patients who don’t receive treatment is less than six months.
If the disease is diagnosed at an early stage, and if the patient meets the surgical and treatment criteria, then their postoperative life expectancy increases to an average of 11.2 months.
The location of the mesothelioma also affects prognosis. Peritoneal mesothelioma often has better survival rates than pleural mesothelioma. In one study:
- Sarcomatoid pleural mesothelioma patients survived for an average of 8 months
- Sarcomatoid peritoneal mesothelioma patients survived for approximately 13 months on average
There are sarcomatoid mesothelioma patients who have significantly outlived their life expectancy. This is thanks to early diagnosis and aggressive treatment.
Learn how survivors beat the odds in our free Mesothelioma Survivor’s Guide.
Frequently Asked Questions About Sarcomatoid Mesothelioma
What does sarcomatoid mesothelioma look like?
Sarcomatoid mesothelioma is difficult to identify in tissue staining and under the microscope. The cells don’t possess a defined structure, but rather an elongated and inconsistent shape. They also can have multiple nuclei, don’t show any clear borders, and don’t always develop in clear patterns or bunches.
How common is sarcomatoid mesothelioma?
Sarcomatoid mesothelioma is diagnosed in 20-30% of cases. It’s most common in pleural mesothelioma and rarely gets diagnosed in peritoneal mesothelioma. Of the approximately 3,000 mesothelioma cases each year in the United States, sarcomatoid mesothelioma makes up no more than 1,000 of them.
What is the survival time for sarcomatoid mesothelioma?
Sarcomatoid mesothelioma has the poorest prognosis of the three cell types. The average life expectancy after diagnosis is 8 months. For patients who receive treatment, the prognosis can improve to 1-2 years.
How is sarcomatoid mesothelioma treated?
Treatment is difficult due to the physical properties of sarcomatoid cells. They don’t clump together, which makes removal during surgery challenging for doctors. Many cancer centers and clinical studies exclude sarcomatoid mesothelioma cases due to these obstacles.
Last Edited: June 1, 2023.
