Sarcomatoid Mesothelioma

Accounting for 7 to 20 percent of all mesothelioma cases, sarcomatoid mesothelioma is the least common of the disease’s three main histological cell types: epithelioid, sarcomatoid and biphasic. This type of tumor has also been called sarcomatous mesothelioma, diffuse malignant fibrous mesothelioma and spindled mesothelioma.

These cells appear elongated, spindle-shaped and often form a fibrous pattern that resembles a tumor called histiocytoma. Some epithelioid cells may be present within sarcomatoid tumors, but by definition, they must make up less than 10 percent of the tumor’s mass.

Variants of this form of cancer include transitional, lymphohistiocytoid and desmoplastic mesothelioma. Like most other types of the disease, the sarcomatoid cell type is linked to asbestos exposure.

Sarcomatoid Is the Most Aggressive Cell Type

About 10 to 20 percent of pleural mesotheliomas and fewer than 4 percent of peritoneal mesotheliomas are made up of this cell type.

• Linked to asbestos exposure.
• Tumors appear as nodules or lesions, with or without effusion, and rarely as a localized mass.
• More resistant to treatment than other cell types.
• Tumors are composed of giant, spindle-shaped cells in fibrous bundles.

Quick Fact:

Most of these tumors develop on the protective lining of the lungs, called the pleura.

Diagnosis

Diagnosing this cell type is difficult because these tumors tend to mimic other benign and malignant conditions in appearance. When pathologists examine these tissue samples under a microscope, the cells resemble those of sarcoma tumors and localized fibrous tumors of the pleura. Because of the aggressive nature of this tumor type, prognosis is not as favorable as other cell types, and treatment options are not as plentiful. The poor survival rates associated with this cell type make accurate diagnosis even more imperative.

Common misdiagnoses for sarcomatoid mesothelioma

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

If a patient’s symptoms and work history suggest an asbestos-related disease, doctors will first order an imaging test such as an X-ray, CT scan or MRI. However, to determine the cell type for a diagnosis, doctors need to retrieve tumor tissue through a biopsy.

If the tissue sample is too small, a pathologist might not be able to see the full extent of the tumor’s features. This could lead to a misdiagnosis. Most sarcomatoid mesotheliomas, for example, contain cells that resemble those of soft tissue tumors (sarcomas).

In 2018, a study was published in the journal Lung Cancer that presented a new approach to differentiate sarcomatoid mesothelioma from fibrous pleuritis. The approach involves immunohistochemistry tests for expression of the BAP1 gene and another gene known as MTAP. The study’s authors concluded the new approach was 100 percent accurate at distinguishing sarcomatoid mesothelioma from fibrous pleuritis.

Symptoms

Symptoms related to this type of cancer are similar to the symptoms of other mesothelioma cell types.

For sarcomatoid mesothelioma of the pleura, symptoms can include shortness of breath, weight loss and weakness. In sarcomatoid mesothelioma of the peritoneum, abdominal “fullness,” pain, anorexia and nausea are common symptoms.

• Shortness of breath
• Prolonged hoarseness
• Persistent cough
• Coughing up blood
• Low oxygen levels
• Anemia
• Weight loss and weakness
• Abdominal “fullness”
• Anorexia and nausea
• Tiredness

Treatment

As with other cell types, treatment usually depends on the stage and location of the cancer. The primary treatment options for this cell type are surgery, chemotherapy and radiation therapy — the same used for other cell types of this cancer.

Surgery

Sarcomatoid cells have proven to be more resistant to treatment than other types of mesothelioma. Surgery in particular can be difficult because these tumors are very rigid and often grow into the chest wall, making them especially difficult to remove. In cases of peritoneal tumors, the cancer usually encases the soft internal organs of the abdomen, which can make the identification and removal of the primary tumor challenging.

Chemotherapy

Chemotherapy has also displayed limited success rates for this cell type. One case report described an encouraging result using a chemotherapy regimen used to treat sarcomas, CYVADIC, which incorporates cyclophosphamide, vincristine, doxorubicin and dacarbazine.

Features and Diagnostic Techniques

Pathological examination reveals these tumors form nodules that invade surrounding tissues, including the fat found in the parietal pleura. When viewed under a microscope, the tissue contains spindle-shaped cells arranged in a haphazard pattern with plump, elongated nuclei. The same pattern is often seen in fibrosarcoma tumors and thus contributes to misdiagnosis. Sometimes sarcomatoid mesothelioma cells can have more than one nucleus, which makes the tumor easily confusable with fibrous histiocytoma.

To better differentiate mesothelioma from other cancers, pathologists use a tissue staining technique called immunohistochemistry. This technique enhances cell samples with diagnostic markers that react to specific proteins in the tumor tissue. Pathologists can look for these reactions under a microscope to make a diagnosis and determine the cancer’s cell type.

A 2015 study explains the most useful markers for diagnosing mesothelioma include cytokeratin 5/6, podoplanin, WT1 and calretinin. The authors of the study add that sarcomatoid tumors may not react to most markers in a majority of cells, however, which makes an accurate diagnosis difficult. They conclude that calretinin and podoplanin are more likely to be effective in diagnosing sarcomatoid mesothelioma, but note a wide variation among laboratories in diagnostic marker choices.

Mesothelioma Variants

Transitional Mesothelioma

This variant behaves like other sarcomatoid mesotheliomas but has plump, spindle-shaped cells.

Lymphohistiocytoid Mesothelioma

Composed of large spindle-shaped cells, lymphohistiocytoid mesothelioma tumors contain a large amount of inflammatory and immune cells mixed throughout. This variant makes up less than 1 percent of all mesotheliomas.

Desmoplastic Mesothelioma

This variant is one of the most difficult cell types to diagnose. At least half of this tumor is “patternless,” and it contains a few elongated cells and collagen bundles. This cell type accounts for approximately 5 percent of all mesotheliomas.

Quick Fact:

Another reason sarcomatoid mesothelioma is difficult to diagnose is that several distinct variants exist.

Prognosis

The median survival for patients with sarcomatoid tumors is typically less than six months, but some patients live longer, depending on factors like age and overall health. Patients with the lymphohistiocytoid variant of this cell type have survived for as long as six years, and there are reports of spontaneous tumor remission.

Finding clinical trials designed for sarcomatoid patients may be difficult. Certain specialty cancer centers, like the UCLA Jonsson Comprehensive Cancer Center in Los Angeles, offer programs dedicated to providing more treatment options and expertise than standard cancer care facilities. Alternative therapies and procedures may be considered if traditional treatment options are exhausted.