This rare subtype was initially described in 1980 and represents 5 to 10 percent of all mesothelioma cases. Its cells are often described as bland or “patternless” in appearance and are usually found once they have invaded the chest wall adipose tissue.
To accurately diagnose any case of an asbestos cancer, a sample of tumor tissue (called a biopsy) is essential. Doctors like to take a large tissue biopsy so that enough cells are reviewed. A large biopsy is particularly important to diagnosing the desmoplastic subtype because fibrous regions of this tumor can hide cell variations that are important to an accurate diagnosis.
The presence of this dense fibrous tissue, in addition to minimal cellularity (patterns formed by cells), characterize the desmoplastic variant of mesothelioma. This pattern makes it challenging for doctors to accurately diagnose desmoplastic malignant mesothelioma (DMM). It’s sometimes misdiagnosed as fibrous pleurisy, pleural fibrosis, rheumatoid disease or spindle cell sarcoma.
Doctors and pathologists have specific criteria to look for when a patient is suspected of having this subtype.
This criterion includes:
- At least 50 percent of the tumor must be made up of dense fibrous tissue that frequently forms nodules
- Areas of increased cellularity that have sarcomatoid mesothelioma characteristics
- Spread of neoplastic spindle cells to the lung or chest wall
- Metastasis to nearby fat tissue, skeletal muscle or the lung
- Presence of the p53 tumor suppressor gene protein
Doctors warn that when this subtype metastasizes, it can look bland and may be confused as benign fibrous tissue. Imaging scans like a CT or MRI may help a pathologist identify spread to the lung or chest wall to diagnose DMM in difficult cases.
In 2017, pathology researchers discovered a protein to help differentiate desmoplastic mesothelioma from sarcomatoid carcinoma of the lung. The protein is called GATA-3. When the protein is present the diagnosis will likely be mesothelioma. If it is absent the diagnosis will likely be lung carcinoma.
Symptoms, Treatment and Prognosis
Although symptoms of mesothelioma are not profoundly affected by the cell type of the tumor, the primary symptom of desmoplastic mesothelioma is chest pain, often caused by a buildup of fluid in the lungs. Treatment for this particular type of mesothelioma is typically not surgical. Treatments for DMM aim to reduce symptoms, prolong survival and improve quality of life without taking aggressive action.
Common treatments include the use of chemotherapy and radiation to shrink tumors and kill cancerous cells. A pleurodesis or paracentesis may be recommended to extract excess fluid from the lungs or abdomen.
Desmoplastic mesothelioma is categorized as a sarcomatoid cancer, which is typified by a poor prognosis. In this case, the life expectancy following diagnosis is usually less than one year. In one seven-year study (1982-1989) that evaluated 255 cases of mesothelioma, researchers identified 17 cases of desmoplastic mesothelioma. Of those, 11 were sarcomatoid and six were biphasic. 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.
Additional research on this rare mesothelioma subtype is needed so that doctors can make a more accurate diagnosis and patients can extend their survival. Desmoplastic patients who are looking for new or unique ways of treating cancer can consider clinical trials and alternative therapies.
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Last Modified July 9, 2019