Sarcomatoid mesothelioma is a rare cell type that accounts for about 10 – 20% of all pleural mesothelioma cases and 4% of peritoneal mesothelioma cases.
Like other forms of the disease, sarcomatoid mesothelioma is caused by asbestos exposure. Because the cells are so rare and also closely mimic other conditions, sarcomatoid mesothelioma is difficult to diagnose early, which can limit a patient’s treatment options. Sarcomatoid cells are also known to metastasize or spread quickly, and typically don’t respond well to treatment. As such, patients diagnosed with sarcomatoid mesothelioma have an average prognosis of six months.
Sarcomatoid Cell Structure
Sometimes referred to as spindle cell mesothelioma, sarcomatoid cells are recognized by their oval, elongated shape with a large nucleus. Because the spindle-shaped cells are oblong, researchers have noted some cells contain multiple nuclei. In many cases, it can be difficult for doctors to recognize sarcomatoid mesothelioma cells, as they closely mimic other healthy cells in the body.
Unlike more common epithelioid cells, which tend to clump together in sheath-like formations, sarcomatoid mesothelioma cells tend to form further apart in nodes or lesions. Because of this, the cells are faster to metastasize to any part of the body compared to other cell types.
Rare Sarcomatoid Cell Types
In some cases, sarcomatoid mesothelioma may also be differentiated as several rare cell types. In general, these cell types are still known for rapid metastasis and a poor prognosis, but may have even more limited treatment options than standard sarcomatoid tumors.
- Desmoplastic mesothelioma: Desmoplastic cells often form without a defined pattern, making diagnosis difficult. Desmoplastic cells are most common in the pleura, but have also been identified in cases of peritoneal and testicular mesothelioma. Patients are typically treated with standard therapies, like chemotherapy, which may also be applied palliatively. Studies have found an average life expectancy of 3.8 months.
- Lymphohistiocytoid mesothelioma: This rare form of mesothelioma accounts for less than 1% of all diagnoses and typically forms in the pleura. Lymphohistiocytic mesothelioma typically has tumors that are made of a variety of cells, including the common epithelial type, immune cells like lymphocytes and plasma cells. Because of the cell makeup, this form of mesothelioma is often confused for non-Hodgkin’s lymphoma, sarcomatoid carcinoma of the lung, and other cancers. Studies have found prognoses ranging from two to 20 months.
- Transitional mesothelioma: Transitional cells are characterized by the typical spindle shape of sarcomatoid cells, though more plump. Studies have said the cells sometimes closely resemble epithelial, making diagnosis difficult. These tumors are extremely rare, with only a few case reports referencing the subtype.
Diagnosing Sarcomatoid Mesothelioma
Properly identifying mesothelioma cell type is an important aspect of the diagnostic process, as cell type is a determining factor for a patient’s prognosis and treatment options. Though making a differentiating diagnosis is challenging for all types and cell types of asbestos cancer, sarcomatoid malignant mesothelioma is especially challenging to accurately diagnose because of its rarity and close resemblance to other conditions, like sarcomatoid carcinoma, soft tissue sarcomas or other fibrous tumors.
As with other forms of the disease, it can take decades for symptoms to first arise after asbestos exposure. Patients may also experience different symptoms depending on where the cancer develops. Most instances of sarcomatoid tumors are found with malignant pleural mesothelioma or malignant peritoneal mesothelioma, which impact the lungs and abdomen, respectively.
Since these cells are also known to spread quickly, sarcomatoid mesothelioma patients may experience worsening symptoms earlier than patients with epithelioid or biphasic cell types.
- Difficulty breathing (dyspnea)
- Abdominal or chest pain
- Excess fluid in the lungs or abdomen
- Nausea and vomiting
- Weight loss
As with all forms of mesothelioma, diagnosis typically begins with imaging tests, including an x-ray and CT scan, to find any visible tumors or identify possible excess fluid in the chest cavity. If cancer is suspected, a blood test will be the next step. There are some biomarkers in the blood that can help identify mesothelioma and differentiate it from other health conditions.
A biopsy is the most important step of the process to make an accurate, differential diagnosis. Taking a fluid or tissue sample is also how a doctor will be able to determine cell type through a number of analyses, like immunohistochemistry. This process entails applying a particular staining method that uses specific antibodies to isolate antigens or proteins in the biopsy 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.
There are a number of markers that can indicate mesothelioma, though studies have found that a cell sample that’s positive for calretinin and D2-40 in combination with the antibody pancytokeratin is the best indicator for sarcomatoid mesothelioma.
In some instances, multiple biopsies and analyses may be necessary to determine if there are just sarcomatoid cells present or if epithelioid cells can also be found, indicating biphasic mesothelioma.
Sarcomatoid Mesothelioma Prognosis
Sarcomatoid mesothelioma has the least favorable prognosis compared to the other common cell types, with studies finding 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, stage at diagnosis, as well as the patient’s age, gender and overall health. These factors will also help determine what treatments may be available to potentially extend survival.
Patients with biphasic mesothelioma may also face a worse prognosis if sarcomatoid cells are more dominant than epithelioid. Biphasic mesothelioma patients typically have a life expectancy of about one year, though may face limited treatment options and a worse prognosis if sarcomatoid cells make up more than 10% of the tumor cells.
Treatment Options for Sarcomatoid Mesothelioma
Most mesothelioma treatment plans entail a multimodal approach of therapies like surgery, chemotherapy and radiation therapy. However, because of the malignant sarcomatoid cells’ structure and aggressive nature, this form of the disease is the least responsive to treatment.
In one case overview of 137 pleural sarcomatoid mesothelioma patients from clinical trials between 2000 and 2014, researchers found only 19 patients had a positive response to treatment and extended life expectancy. Overall, sarcomatoid mesothelioma patients had an average response rate of 13.9%, compared to an overall response rate of 21.9% across all types of mesothelioma.
Because the cancer is difficult to diagnose in its early stages, surgical resection of sarcomatoid mesothelioma tumors is rarely a viable option. Most patients aren’t properly diagnosed until the disease has metastasized distantly, making surgery too risky. Researchers have noted that even for patients who have been treated with surgery, the treatment often does little to impact survival rate. One study of 224 sarcomatoid mesothelioma patients found an average prognosis of four months with surgical resection.
Mesothelioma specialists may instead rely on chemotherapy combinations as a first line of treatment. However, chemotherapy has shown limited success, as the cells are resistant to the treatment. Radiation therapy may also be applied in some cases, often as a palliative treatment to lessen symptoms and improve a patient’s comfort.
Due to the rarity of sarcomatoid cells, patients and their loved ones may have difficulties finding clinical trials specifically designed for the cell type. However, patients may still be eligible to join various studies depending on the location of their disease, stage and any previous treatments.Sources
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