Desmoplastic mesothelioma is a cellular subtype of mesothelioma that occurs in the pleura and sometimes in the peritoneum. It is classified as a fairly common variant of sarcomatoid mesothelioma – an aggressive cell type – but cases of cosmoplastic mesothelioma with biphasic and epithelial cells are diagnosed on rare occasions.
This rare subtype was first described in 1980 and represents 5 to 10% of all mesothelioma cases. Its cells are often described as having a bland or “no pattern” appearance and are usually found once they have invaded the adipose tissue of the chest wall.
To accurately diagnose any case of asbestos cancer, a sample of tumor tissue (called biopsy) is essential. Doctors prefer to perform a large tissue biopsy to control the number of cells. A large biopsy is particularly important to diagnose the desmoplastic subtype, as the fibrous regions of this tumor can mask important cellular variations for accurate diagnosis.
The presence of this dense fibrous tissue, besides minimal cellularity (cell-shaped patterns), characterizes the desmoplastic variant of mesothelioma. This trend makes it difficult for physicians to accurately diagnose desmoplastic malignant mesothelioma (DMM). It is 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% of the tumors should consist of dense fibrous tissue that frequently forms nodules.
Areas of Increased Cellularity that Have Sarcomatoid Mesothelioma Features
Propagation of neoplastic fusiform cells to the lung or chest wall
Metastases to adjacent adipose tissue, skeletal muscle or lung
Presence of the p53 tumor suppressor gene protein
Doctors warn that when this subtype is metastasized, it may seem bland and be mistaken for benign fibrous tissue. Imaging such as computed tomography or MRI can help a pathologist identify the spread in the lungs or chest wall to diagnose DMM in difficult cases.
Symptoms, treatment, and prognosis
Although the symptoms of mesothelioma are not profoundly affected by the cell type of the tumor, the main symptom of desmoplastic mesothelioma is chest pain, often caused by fluid accumulation in the lungs. The treatment of this particular type of mesothelioma is usually not surgical. The treatments for DMM are aimed at reducing symptoms, prolonging survival and improving quality of life without taking aggressive measures.
Common treatments include the use of chemotherapy and radiation therapy to reduce tumors and kill cancer cells. Pleurodesis or paracentesis may be recommended to remove excess fluid from the lungs or abdomen.
Desmoplastic mesothelioma is classified as sarcomatoid cancer, which has a poor prognosis. In this case, life expectancy after diagnosis is usually less than one year. In a seven-year (1982-1989) study of 255 mesothelioma cases, the researchers identified 17 cases of desmoplastic mesothelioma. Of these, 11 were sarcomatoid and six biphasic. Mean survival from onset of symptoms at death was 5.8 months for the sarcomatoid variant and 6.8 months for the biphasic variant.
Further research on this rare subtype of mesothelioma is needed so that doctors can make a more accurate diagnosis and patients can extend their survival. Patients desmoplastic looking for new or unique ways to treat cancer may consider clinical trials and alternative therapies.