Sarcomatoid mesothelioma is the rarest cell type of the cancer, accounting for between 10% and 20% of all cases.
Written by Jenna Campagna, RN
Jenna Campagna, a registered nurse and medical expert, wrote this page to ensure accurate, complete and clear information is delivered to readers. You can find more information on Mesothelioma Guide's process for creating content, fact-checking and making revisions on our Editorial Practices and Guidelines page.
What Is Sarcomatoid Mesothelioma?
Sarcomatoid Cell Type
Sarcomatoid mesothelioma is a cellular type of the rare cancer. It’s also called “fibrous” due to its appearance.
This form of mesothelioma involves faster metastasis, meaning tumors often spread to other areas of the body. The sarcomatoid form is the least treatable cell type, though new treatments are leading to longer life expectancies.
Characteristics of Sarcomatoid Mesothelioma Cells
Sarcomatoid cells are spindle-shaped, meaning they look long and narrow. They have enlarged, elongated nuclei. These cells sometimes have more than one nucleus and are harder to distinguish from healthy tissue.
Sarcomatoid cells do not form in regular patterns like epithelioid cells do. Instead, they proliferate through soft tissue, where the cells are much more 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 a subtype called mesothelial cells.
When asbestos fibers reach these linings, they can lodge into and irritate the mesothelial cells. This is how mesothelioma forms.
Many of the diseased cells remain epithelial cells, which is why epithelioid mesothelioma is the most common cellular type of the cancer. 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, the latter of which is part of the body’s connective tissue (such as bones and cartilage).
Connective tissue cells that become cancerous are called sarcomas, which is the origin of the name sarcomatoid mesothelioma. Epithelioid cells can be present in sarcomatoid mesothelioma but must comprise less than 10% of the tumors’ cells. If the amount is 10% or higher, then the cancer is considered biphasic.
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 sometimes mimic those caused by other illnesses. This is one of the reasons why early detection is so vital for mesothelioma patients since the disease is less treatable in later stages.
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
a Mesothelioma Cancer Center
Specializes in Pleural and Peritoneal Mesothelioma
Sarcomatoid mesothelioma is difficult to identify because of how infrequently patients develop this cell type. Doctors are not familiar with sarcomatoid mesothelioma and cells can look similar to benign tissue.
In order for doctors to get a definitive diagnosis after initial imaging scans, they will need to perform a fluid extraction or tissue biopsy.
Since this kind of mesothelioma is difficult to identify and the concentration of malignant cells in the biopsy might be too low to detect, the initial microscopic analysis might be inconclusive.
If the biopsy is adequate, pathologists will use what is called immunohistochemistry to accurately define the cell type. This process involves tissue staining to make proteins in the cell samples more recognizable. Doing so gives pathologists a way to more precisely diagnose patients with this rare form of mesothelioma.
Immunohistochemical markers looked for when diagnosing sarcomatoid mesothelioma include:
- Podoplanin (D2-40)
Patients diagnosed with mesothelioma, particularly with less common cell types like sarcomatoid, should seek a second opinion. Having a mesothelioma specialist analyze the results of diagnostic tests can make all the difference when planning the best treatment.
The long latency period of mesothelioma, along with its aggressive behavior once the tumors form, can lead to a misdiagnosis. Many general physicians are less experienced in identifying mesothelioma and will attribute the symptoms and test results to more common illnesses.
Surgery, chemotherapy and radiation are treatment options most often used with mesothelioma patients. However, surgery can be ineffective for sarcomatoid mesothelioma. The scattered growth pattern of sarcomatoid cells makes surgical removal extremely difficult.
The cells don’t clump together like epithelioid mesothelioma cells do. This is why there are strict criteria for surgical candidates based on the level of metastasis around the point of origin.
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.
Radiation is another treatment option, although it’s often used as a second-line treatment either before or after surgery or chemotherapy. Radiation can be used for pain-relief purposes.
Subtypes of Sarcomatoid Mesothelioma
There are three subtypes of sarcomatoid mesothelioma. The specific subtype of the cancer can also affect the treatment a patient receives. Certain subtypes are less responsive to traditional treatments and add a layer of complexity to the diagnostic process.
- Transitional mesothelioma
- Lymphohistiocytoid mesothelioma
- Desmoplastic mesothelioma
The prognosis for sarcomatoid mesothelioma is not as positive 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 6 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 the prognosis. Peritoneal mesothelioma often has better survival rates than pleural mesothelioma:
- Sarcomatoid pleural mesothelioma patients survived for an average of 8 months.
- Sarcomatoid peritoneal mesothelioma patients survived for approximately 13 months on average.
There are patients diagnosed with sarcomatoid mesothelioma who have significantly outlived their life expectancy after receiving treatment. Identifying the disease at the earliest possible stage is essential to achieving an optimistic prognosis.
Learn how survivors beat the odds in our free Mesothelioma Survivor’s Guide.
Common 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: January 15, 2021.