Desmoplastic Mesothelioma

Desmoplastic mesothelioma is a cell subtype of mesothelioma that occurs in the pleura and occasionally in the peritoneum. It is classified as a fairly common variant of sarcomatoid mesothelioma - an aggressive cell type - but cases of desmoplastic mesothelioma with biphasic and epithelial cells are diagnosed on rare occasions.

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.

Diagnosing Desmoplastic Mesothelioma

To accurately diagnose any case of mesothelioma, a sample of tumor tissue (called a biopsy) is essential. Doctors are recommended 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 a desmoplastic diagnosis.

The presence of this dense fibrous tissue in addition to minimal cellularity (patterns formed by cells) makes it challenging for doctors to diagnose desmoplastic malignant mesothelioma (DMM). It’s sometimes misdiagnosed as fibrous pleurisy, pleural fibrosis, rheumatoid disease and spindle cell sarcoma.

Doctors and pathologists have specific criteria to look for when a patient is suspected of having desmoplastic mesothelioma.

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 mesotheliomacharacteristics
• Specific areas of cell death, known as necrosis, are seen in 70 percent of cases
• 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 desmoplastic mesothelioma 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.

Fast Fact: In a study that analyzed 709 cases of mesothelioma from 1998 to 2002, the desmoplastic subtype was diagnosed in 2 percent of cases - less than the average 5 to 10 percent typically diagnosed.

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 palliative, which aims 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.