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What Is Sarcomatoid Mesothelioma?

Sarcomatoid mesothelioma is the rarest and most challenging to treat variant of the disease’s three primary tumor cell types. Compared to epithelial and biphasic mesothelioma, it is also the most aggressive and resistant to treatment. Inhaling asbestos fibers causes mutations in mesothelial cells that can develop into sarcomatoid mesothelioma.

Sarcomatoid mesothelioma

The term sarcomatoid is the general classification for sarcomatous, spindle or diffuse malignant fibrous mesothelioma. Sarcomatoid tumors can merge to form a sheet-like, fibrous mass on the pleural membrane.

Treating the spindle cell variant is more challenging than other types of mesothelioma because the tumor cells are resistant to therapy and quickly spread or metastasize to new areas. 

Tumors with this cell type appear fibrous and diffuse throughout the pleura, the term for the pleural membrane surrounding the lungs and lining the chest cavity. 

Sarcomatoid Mesothelioma Facts

The characteristics of sarcomatoid cells make this variant of mesothelioma especially difficult to treat. Pathologists who specialize in mesothelioma are able to identify some of these rare cellular features when viewing tissue samples under a microscope.

  • Spindle cells appear long, oval and spindle-shaped.
  • The center, or nucleus, of sarcomatoid cells is often enlarged and elongated. Some cells may have more than one nucleus.
  • Nearly all sarcomatoid mesotheliomas are pleural. There are fewer than 30 documented cases of sarcomatoid peritoneal mesothelioma.
Karen Selby, RN, patient advocate for the Mesothelioma Center
“If you’ve been diagnosed with mesothelioma, I would encourage you to not look at those statistics and life expectancies and think that is your future. Everyone is different with this diagnosis. It’s really important to speak to those specialists who deal with this disease to determine what your future is going to be.”
Karen Selby
Registered nurse and Patient Advocate at The Mesothelioma Center at Asbestos.com

Rare Sarcomatoid Mesothelioma Cell Subtypes

Epithelial, biphasic and sarcomatoid are the three primary cell types of mesothelioma tumors. Within each variant, cells may have different characteristics that pathologists further classify into subtypes. There are three rare sarcomatoid mesothelioma cell subtypes.

Transitional Mesothelioma: This variant tends to grow and spread in ways similar to other sarcomatoid mesotheliomas. It has fat, spindle-shaped cells, which helps pathologists differentiate it from other cells.

Lymphohistiocytoid Mesothelioma: These tumors contain inflammatory and immune cells. The lymphohistiocytoid variant makes up less than 1% of all mesotheliomas. Some patients with this cancer have a better-than-average life expectancy.

Desmoplastic Mesothelioma: This sarcomatoid subtype is one of the most difficult to diagnose. Half or more of the tumor shows no discernible pattern of growth. Desmoplastic type accounts for approximately 5% of all mesotheliomas.

Dr. Jacques Fontaine, pleural mesothelioma doctor and expert contributor for Asbestos.com
“Sarcomatoid cell types – these are slightly more aggressive tumors.”
Dr. Jacques Fontaine

Symptoms of Sarcomatoid Mesothelioma

Because sarcomatoid mesothelioma is almost exclusively found in the pleural membrane, most patients experience nonspecific respiratory symptoms such as cough and shortness of breath. Common symptoms include:

  • Shortness of breath
  • Prolonged hoarseness
  • Persistent cough
  • Coughing up blood
  • Low blood oxygen levels
  • Anemia (low iron)
  • Weight loss and weakness
  • Chest pain or abdominal fullness
  • Lack of appetite, anorexia and nausea
  • Fatigue and extreme tiredness

Patients also commonly experience chest pain prior to diagnosis. As the disease progresses, symptoms become more serious. It’s important to speak with a specialist about any history of first or possible secondhand asbestos exposure and symptoms as early as possible.

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Diagnosis of Sarcomatoid Mesothelioma

Mesothelioma is unfortunately often misdiagnosed because signs of the disease mimic other, less severe conditions.

A 2018 study described a new approach for a more accurate sarcomatoid malignant mesothelioma diagnosis. Tests for the BAP1 and MTAP genes were 100% accurate for distinguishing sarcomatoid mesothelioma from fibrous pleuritis.

However, since genetic testing for mesothelioma requires further clinical trials before widespread adoption, most doctors still favor traditional diagnostic methods.

Misdiagnosing Sarcomatoid Mesothelioma

Physicians inexperienced with sarcomatoid mesothelioma tend to misdiagnose the disease as other types of thoracic or lung cancer.

Common misdiagnoses include:

  • Pleural liposarcoma
  • Fibrous pleurisy or pleuritis
  • Sarcoma or fibrosarcoma
  • Malignant fibrous histiocytoma (also called undifferentiated pleomorphic sarcoma)
  • Localized fibrous tumors
  • Metastasized renal cell carcinoma
  • Solitary fibrous tumor of the pleura (hemangiopericytoma)

Seeking a second opinion from a mesothelioma specialty team is essential for sarcomatoid patients because this group will include pathologists skilled in this diagnosis.

Imaging Scans

As part of the initial diagnostic procedure, doctors rule out causes of ongoing symptoms using physical exams and in-office testing. Then, they will order imaging studies such as X-rays, CT scans or MRIs. These tests reveal abnormalities in the chest, but they do not show specific details such as cell type.

Biopsies

If your imaging studies suggest cancer, your doctor will refer you for a biopsy where a surgeon collects a small tumor sample for analysis and identification under a microscope. Depending on the type of biopsy, physicians can obtain tumor tissue samples using a needle under CT scan guidance or in an outpatient procedure with anesthesia.

Surgeons often use thoracoscopy or video-assisted thoracic surgery procedures to biopsy mesothelioma. These techniques result in high-quality tissue samples that can increase the chances of an accurate diagnosis. 

Immunohistochemistry

Specific tests called immunohistochemistry reveal the cancer cell type and stage from a biopsy. Immunohistochemistry involves staining the cells using antibodies that attach to antigens on the tumor. This method indicates to pathologists whether the cancer is benign or malignant. These protein markers include calretinin, podoplanin, D2-40 and pan-cytokeratin. 

Prognosis for Sarcomatoid Mesothelioma

The life expectancy for patients with sarcomatoid mesothelioma ranges from 4 to 18 months with treatment. Without treatment the median survival for patients with sarcomatoid tumors is typically less than six months.

Each patient’s prognosis differs based on the stage and location of the cancer and overall patient health.

Sarcomatoid cells are notoriously resistant to treatment because of their fibrous nature. Current treatments, however, have helped several patients with the lymphohistiocytoid cell subtype survive for up to four years, and one documented patient remained alive without symptoms 12 years after his diagnosis.  

It’s important to note that doctors use past data to make prognosis estimates. As treatment options improve and newer, cutting-edge therapies are employed, prognosis typically improves as well. Current survival rate statistics don’t take this most recent data into account. 

Clinical trials offer the best chance at improving prognosis and are available at specialized centers. Patients interested in the newest available therapies should seek treatment at a specialty mesothelioma treatment facility.

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Sarcomatoid Mesothelioma Treatment

The best mesothelioma treatment options for the sarcomatoid cell type include immunotherapy, chemotherapy, targeted therapy and radiation therapy. Patients should seek care from a mesothelioma specialist because sarcomatoid mesothelioma is harder to treat than the epithelioid or biphasic cell types.

Surgeons generally do not operate on patients with this type of mesothelioma because sarcomatoid cancer cells tend to return within a few months of the procedure.

There is currently no cure for sarcomatoid or any other variant of mesothelioma. Treatment can improve cancer symptoms, extend survival and increase quality of life for many patients.

Karen Selby, RN, patient advocate for the Mesothelioma Center
“There are many variants of mesothelioma, sarcomatoid being one of the rarest and potentially trickiest to treat. The Patient Advocates here at The Mesothelioma Center can assist the patient in connecting with a specialist who can successfully diagnose and also craft the best overall treatment plan based on the uniqueness of the patient’s needs.”
Karen Selby, R.N.
Patient Advocate at The Mesothelioma Center

Immunotherapy

Nivolumab and ipilimumab, also known by the brand names Opdivo and Yervoy, are part of an FDA-approved immunotherapy combination for mesothelioma, including the sarcomatoid cell type.

This drug combination has improved the median overall survival of patients by four months compared to those receiving chemotherapy. It became the new first-line treatment for inoperable mesothelioma in 2020.

Chemotherapy

If immunotherapy stops working, the standard chemotherapy for treating pleural sarcomatoid mesothelioma is a combination of pemetrexed (Alimta) plus cisplatin or carboplatin. This treatment regimen is also the standard chemotherapy for patients with any cell type of malignant pleural mesothelioma.

Targeted Therapy

AZD8186 is an experimental targeted therapy drug that is effective with some cancers when combined with other targeted drugs or chemotherapy. Research in mice suggests a combination of AZD8186 and the targeted drug selumetinib may be successful in patients with sarcomatoid malignant mesothelioma.

Radiation Therapy

Radiation therapy is not considered curative for mesothelioma, but for patients with painful tumors penetrating the chest wall it can reduce pain and improve quality of life.

Surgery

A 2020 study published in Translational Lung Cancer Research confirms surgeons do not operate on patients with sarcomatoid mesothelioma because sarcomatoid tumors recur quickly after surgery.

Sarcomatoid tumors are rigid, and they often spread over large areas and into the chest wall, which makes it challenging to remove all cancerous cells through surgery. Similarly, in the abdomen, peritoneal mesothelioma tumors can grow into or encase the soft internal organs.

Sarcomatoid cancer cells tend to return quickly, even after extensive surgery, because it is harder to remove sarcomatoid tumors compared to epithelioid tumors. Patients with epithelioid tumors may live for years after surgery, where sarcomatoid patients tend to live for only a few months. Surgeons do not consider a few months enough of a survival benefit to justify the risks of surgery.

Common Questions About Sarcomatoid Mesothelioma

Is sarcomatoid a type of mesothelioma?

Sarcomatoid mesothelioma is a variant of the disease that involves the rarest of three tumor cell types. Other mesothelioma tumor cell types include epithelial and biphasic, which describe the type of cells within a patient’s tumor. Sarcomatoid mesothelioma cancer cells appear long and spindle-shaped, forming diffuse and fibrous tumors throughout the pleura.

What do I need to know about sarcomatoid mesothelioma?
  • Sarcomatoid is the most aggressive and fastest spreading mesothelioma cell type and has the lowest average survival rate.
  • It makes up 10% to 20% of all mesothelioma cases.
  • It is more resistant to treatment than other types.
  • However, clinical trials are testing new therapies for sarcomatoid mesothelioma that may be available to you through your physician.
How do I find a doctor who treats sarcomatoid mesothelioma?

All mesothelioma doctors have studied sarcomatoid mesothelioma and received training on how to treat this specific cell type. These specialists know the right kind of treatments and approaches that best control sarcomatoid mesothelioma. They also can connect you to clinical trials designed for patients with this cell type.


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