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What Is Desmoplastic Mesothelioma?

Desmoplastic mesothelioma is a subtype of the sarcomatoid form of mesothelioma. Sarcomatoid refers to long and spindle-shaped cells that develop into a rarer and more deadly form of mesothelioma cancer.

The presence of dense fibrous tissue with reduced cellular features characterizes the desmoplasia variant of this cancer. This subtype has a poor prognosis and can occur in all types of sarcomatoid mesothelioma.

Under a microscope, desmoplastic cells are not well-differentiated and lack defining qualities or patterns. These types of mesothelioma cells form dense fibrous nodules of hyalinized connective tissue within tumors, making diagnosis more challenging.

This rare variation is present in 5% to 10% of all malignant mesothelioma cases, and asbestos exposure is the disease’s primary cause.

Diagnosing Desmoplastic Mesothelioma

When diagnosing mesothelioma, a sample of tumor tissue collected from a biopsy is essential for determining cell type and treatment options. Doctors typically take a substantial tissue sample so they can review enough cells to make a diagnosis.

A large biopsy is especially essential to diagnosing desmoplastic malignant mesothelioma because fibrous regions of this tumor can hide cell variations that are important to an accurate diagnosis.

This characteristic makes it challenging for doctors to diagnose desmoplastic malignant mesothelioma, or DMM, accurately. Physicians sometimes misdiagnose desmoplastic malignant pleural mesothelioma as fibrous pleurisy, pleural fibrosis, rheumatoid disease or spindle cell sarcoma.

Fortunately, doctors and pathologists have specific diagnostic criteria to look for when investigating whether a patient has this subtype.

Desmoplastic Mesothelioma Diagnostic Criteria

  • At least 50% of the tumor frequently forms nodules of dense fibrous tissue.
  • Areas of increased cellularity are present with sarcomatoid characteristics.
  • Neoplastic spindle cells have spread to the lung or chest wall.
  • Metastasis has occurred in nearby fat tissue, skeletal muscle or the lung.
  • The p53 tumor suppressor gene protein is present.

When desmoplastic mesothelioma spreads to other areas, it can look bland and cause doctors to mistake the cells as benign fibrous tissue. Imaging scans such as a CT or MRI may help pathologists identify metastasis and diagnose DMM in challenging cases.

In 2017, pathology researchers discovered a protein called GATA-3 that differentiates desmoplastic mesothelioma from sarcomatoid lung cancer. The protein is present in many mesothelioma cells and typically absent in lung carcinoma cases, aiding physicians when staging pleural mesothelioma.

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Symptoms of Desmoplastic Mesothelioma

The primary characteristic of desmoplastic malignant mesothelioma is a high concentration of fibrous connective tissue. These dense and fibrous areas can produce symptoms similar to pulmonary fibrosis, such as chest pain and a buildup of fluid in the lungs. However, this can vary based on the different areas where mesothelioma tumors develop.

However, symptoms of mesothelioma are not significantly affected by the tumor’s cell type. Pleural mesothelioma patients will typically experience shortness of breath, and peritoneal patients often present with abdominal pain.

Desmoplastic Mesothelioma Treatment

Treatment options for desmoplastic mesothelioma depend on the patient’s age and overall health. The most common treatment options include immunotherapy, chemotherapy and radiation therapy, which can kill cancerous cells to shrink tumors and limit spreading.

Immunotherapy with the combination of nivolumab (Opdivo) and ipilimumab (Yervoy) is considered first-line treatment, followed by chemotherapy with cisplatin and pemetrexed (Alimta). Radiation may be used to shrink painful chest wall tumors.

This type of mesothelioma is rarely treated with surgery because it has a high risk of returning within several months of the procedure. Most patients do not benefit from surgery, so it is extremely rare for a surgeon to recommend it to desmoplastic patients. A few case reports of desmoplastic patients with early-stage or localized tumors show some patients lived several months longer following surgery.

Treatments for desmoplastic mesothelioma aim to reduce symptoms, prolong survival and improve quality of life. Doctors often recommend pleurodesis or paracentesis to extract excess fluid from the lungs or abdomen.  

Prognosis of Desmoplastic Mesothelioma

The prognosis of mesothelioma with desmoplasia is not favorable, similar to other types of sarcomatoid cancer. The disease subtype is notoriously tricky to diagnose, and patients often have advanced disease at diagnosis. The life expectancy of patients with this subtype is typically less than one year.

In one seven-year study that evaluated 255 patients with mesothelioma between 1982 and 1989, researchers identified 17 cases of the desmoplastic subtype. Of those, 11 were sarcomatoid and six were biphasic, comprising both sarcomatoid and epithelial cell types.

The mean survival from the onset of symptoms to death was 5.8 months for the sarcomatoid variant and 6.8 months for the biphasic variant. Other studies have suggested an average life expectancy of 3.8 months for desmoplastic malignant mesothelioma patients.

These types of mesothelioma cells form dense fibrous nodules of hyalinized connective tissue within tumors, making diagnosis more challenging.

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