Sarcomatoid mesothelioma is a rare cell type caused by asbestos exposure. It accounts for approximately 10 – 20% of all mesothelioma diagnoses. Sometimes referred to as spindle cell mesothelioma, sarcomatoid cells are recognized by their oval, spindle shape. This cell type typically forms in separate nodes or lesions and can metastasize, or spread, quickly to distant organs. It is also the most difficult cell type to treat, with an average prognosis of six months.
What Is Sarcomatoid Mesothelioma?
Sarcomatoid mesothelioma is a less common cell type. It accounts for about 10 – 15% of all pleural mesothelioma diagnoses and 4% of peritoneal mesothelioma diagnoses.
There are several defining characteristics that can help identify sarcomatoid cells:
- An oval, elongated shape with a large nucleus
- Multiple nuclei in some cells
- Unstructured formation in fibrous nodes or lesions
- Distant cell formation that is faster to metastasize than other cell types
- Because sarcomatoid cells are notable for their oblong, spindle shape, sarcomatoid mesothelioma is also referred to as spindle cell or sarcomatous mesothelioma.
Compared to other mesothelioma cell types, malignant sarcomatoid cells are more aggressive. This type of mesothelioma cancer is also considered more difficult to diagnose and treat. Sarcomatoid cells mimic healthy cells and are also frequently misdiagnosed.
Sarcomatoid Mesothelioma Symptoms
Malignant sarcomatoid mesothelioma symptoms may take 10 – 50 years to develop. Patients may experience different symptoms depending on where the cancer develops.
Sarcomatoid cells are most common in malignant pleural mesothelioma, which impacts the lining of the lungs. In rare cases, patients may be diagnosed with sarcomatoid peritoneal mesothelioma. This type of mesothelioma develops in the abdominal lining.
Because malignant sarcomatoid cells spread quickly, sarcomatoid patients may experience worsening symptoms earlier than patients with epithelioid or biphasic cell types.
Diagnosing Sarcomatoid Mesothelioma
Properly identifying mesothelioma cell type is an important aspect of the diagnostic process. Sarcomatoid malignant mesothelioma is difficult to accurately diagnose because of its rarity and resemblance to other conditions.
Diagnosis typically begins with imaging tests, including an X-ray and CT scan. These tests will identify any visible tumors or excess fluid in the chest cavity. If cancer is suspected, doctors may order a blood test. This test identifies biomarkers that can differentiate mesothelioma from other conditions.
A biopsy is the most important step in making an accurate sarcomatoid mesothelioma diagnosis. Cell type can be determined through a tissue biopsy and analyses of the sample, such as immunohistochemistry. This is a staining method that uses specific antibodies to isolate antigens or proteins in the tissue sample.
Through an immunohistochemical stain, a pathologist can identify if a tumor is benign or malignant, as well as determine cell type, stage and prognosis.
Several immunohistochemical markers can indicate mesothelioma. Studies have found stains that test positive for proteins calretinin and D2-40, in combination with the antibody pancytokeratin, are the most accurate indicator of sarcomatoid mesothelioma.
Multiple biopsies may be necessary to determine if a patients’ tumors solely exhibit sarcomatoid cells. In some cases, epithelioid cells may also be present, indicating biphasic mesothelioma. Additional tests may also be needed to make an accurate differential diagnosis.
Common misdiagnoses of sarcomatoid mesothelioma include:
Fibrous pleurisy Fibrous tumors Fibrosarcoma Metastasized renal sarcoma Non-Hodgkin’s lymphoma Pleural liposarcoma Sarcomatoid carcinoma Soft tissue sarcomas
Rare Sarcomatoid Cell Types
In some cases, sarcomatoid mesothelioma may also be differentiated as several rare cell types. These cell types are known for rapid metastasis and poor prognosis. These subtypes may have even more limited treatment options than standard sarcomatoid tumors.
- Desmoplastic mesothelioma: Desmoplastic cells often form without a defined pattern. Desmoplastic mesothelioma is most common in the pleura (lining of the lungs), but has also presented in cases of peritoneal and testicular mesothelioma. It accounts for about 5% of all diagnoses. Studies have found an average life expectancy of 3.8 months.
- Lymphohistiocytoid mesothelioma: This rare form accounts for less than 1% of all diagnoses. It typically forms in the pleura. Lymphohistiocytoid mesothelioma indicates tumors are made of a variety of cells, including epithelial cells and immune cells, such as lymphocytes and plasma cells. Studies have found an average survival time of two to 20 months.
- Transitional mesothelioma: Transitional cells develop similarly to other subtypes, but are characterized by a plump spindle shape. The cells sometimes closely resemble epithelial cells, making diagnosis difficult. These tumors are rare, with only a few case reports referencing the subtype.
Sarcomatoid Mesothelioma Prognosis
Sarcomatoid mesothelioma has the least favorable prognosis compared to the other common cell types. Studies have shown life expectancies ranging from one month to about 28 months. The majority of patients face a median survival of six months or less.
An individual’s prognosis will also depend on the type of mesothelioma and stage at diagnosis, as well as the patient’s age, gender and overall health.
Patients with biphasic mesothelioma may face a worse prognosis if sarcomatoid cells are more dominant than epithelioid. Biphasic mesothelioma patients typically have a life expectancy of about one year. However, if sarcomatoid cells make up more than 10% of the tumor, patients may have more limited treatment options and a worse prognosis.
Sarcomatoid Mesothelioma Treatment
Research shows sarcomatoid mesothelioma is the most difficult to treat of all cell types. Studies suggest the cells are resistant to many standard therapies. Because malignant sarcomatoid mesothelioma spreads quickly throughout the body, surgery may not be a viable option for many patients.
Chemotherapy is often a first-line treatment for sarcomatoid mesothelioma. Though some studies show the cells can be resistant to chemotherapy, research suggests the treatment may extend survival in some cases.
One study examined 137 pleural sarcomatoid mesothelioma patients between 2000 and 2014. Researchers found:
19 patients had a positive response to chemotherapy treatment, meaning disease progression slowed or stopped during treatment.
Patients with positive responses received chemotherapy as a first-line treatment.
Sarcomatoid patients experienced a 13.9% response rate compared to a 21.9% response rate across all types of mesothelioma.
Immunotherapy treatments have also shown promise in clinical trials for sarcomatoid mesothelioma. Early research suggests it may be an effective option for patients with sarcomatoid mesothelioma who previously received chemotherapy. Some early evidence indicates sarcomatoid mesothelioma may be more responsive to immunotherapy than other cell types.
Radiation therapy may also be applied in some cases. It is often used as a palliative treatment to lessen symptoms and improve a patient’s quality of life.
Research continues to investigate possible treatment combinations to improve life expectancy for sarcomatoid mesothelioma patients.