Desmoplastic Mesothelioma
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Mesothelioma has three main cellular sub-types. Most mesothelioma tumors are made up of epithelial cells. Biphasic and sarcomatoid (the least common) are the two sub-types. Biphasic tumors contain a mixture of sarcomatoid and epithelioid cells. Sarcomatoid types make up only about 15 percent of all cases. Even rarer is a subtype of sarcomatoid mesothelioma called desmoplastic mesothelioma.
Desmoplasia refers to the growth of connective and fibrous tissue. However, this type of mesothelioma is not always associated with malignant cancer. Therefore, a malignant mesothelioma of this sub-type is often misdiagnosed as benign. Diagnosis is important for desmoplastic mesothelioma. Since tumor mostly composed of dense hyalinized fibrous stromal cells and a few malignant cells, the diagnosis of desmoplastic mesothelioma is difficult. They tend to be diagnosed when they invade to the chest wall adipose tissue. Like all sarcomatoid mesotheliomas, this sub-type is aggressive and spreads quickly.
Desmoplasia
The term desmoplasia refers to any type of growth of fibrous connective tissue. It is typically a reactive growth that begins in response to something like a tumor or scar tissue. Although the fibrosis is not always malignant, it does usually invade surrounding healthy tissue, which can be problematic. When mesothelioma is the desmoplastic sub-type, this invasion of the fibrosis is often what leads to a diagnosis.
Characteristics of Desmoplastic Mesothelioma
Desmoplastic mesothelioma accounts for just 5 percent of asbestos-related mesothelioma. Because it is rare, desmoplastic mesothelioma is not well understood. However, one study found that about 88 percent of people diagnosed had already experienced metastases. This is typical of all types of sarcomatoid mesothelioma, which are generally more aggressive than epithelial cancers.
Under the microscope, the tumor’s appearance includes dense bundles of collagen fibers. Collagen fibers are a type of connective tissue. Even when the collagen fibers had a spindled order, arrangement was typically irregular. This characteristic can be useful in diagnoses. Seventy-five percent of desmoplatic mesothelioma cases showed collagen death, appearing on the cellular level as bland and without inflammation.
Apart from histological characteristics, desmoplastic mesothelioma causes symptoms similar to other types of mesothelioma. Most cases are pleural, causing shortness of breath, coughing, and chest pain. Some cases have been found to be peritoneal mesothelioma. Peritoneal mesothelioma causes abdominal swelling, pain, and indigestion. This sub-type has even been seen, though very rarely, in pericardial mesothelioma.
Diagnosis
Generally, any mesothelioma diagnosis begins with a physical exam followed by imaging tests like X-rays and CT scans. If images show unusual tissue growth, a biopsy will be taken. A biopsy is the removal of a small amount of fluid or tissue from the tumor which is then examined under a microscope. A pathologist will determine the cancer type and, if it is mesothelioma, the sub-type.
Diagnosing desmoplastic mesothelioma can be tricky. The tissue looks bland and closely resembles benign fibrous tissue. For this reason, malignant desmoplastic mesothelioma may be misdiagnosed as pleural fibrosis. One study suggest that conventional pleural biopsy is not as good as wedge lung resection at diagnosing desmoplastic mesothelioma. Some diagnostic criteria used to confirm desmoplastic mesothelioma include dense fibrous tissue in more than half of the tumor. There must also be features of sarcomatoid cancer, collagen tissue death, and an invasion of surrounding tissue by the tumor.
One study investigated over 300 cases of sarcomatoid mesothelioma, finding immunohistochemistry particularly useful in diagnosis. Stromal invasion can be shown by pancytokeratin staining. Fatlike spaces can be seen and S100 protein, laminin, and collagen IV markers can be used to distinguish adipose tissue and fatlike spaces.
This diagnostic technique, which uses antibodies and tissue samples from a biopsy, has been used to distinguish different sub-types of sarcomatoid mesothelioma, including desmoplastic mesothelioma. Antibodies are proteins of the immune system that normally detect pathogens. However, antibodies can also be used to detect proteins called antigens that are specific to different cancer cell types.
Treatment
As with any mesothelioma, treatment for desmoplastic mesothelioma varies depending on the cancer stage, the patient age and health. The three most common treatment types are chemotherapy, radiation, and surgery. Surgery is less commonly used because desmoplastic mesothelioma has usually already metastasized.
There is currently no treatment for DMM, but patients are generally treated according to Malignant pleural mesothelioma (MPM) guidelines which is chemotherapy. Chemotherapy and radiation can be used to shrink the tumors. Radiation, targeted to specific tumors, causes fewer side effects. On the other hand, chemotherapy is systemic, meaning it affects the entire body, attacking all cells that divide rapidly. This makes it more effective than other treatments. The present regimen for DMM chemotherapy consists of cisplatin plus pemetrexed. However chemotherapy has many unpleasant side effects because it also affects healthy cells in the body.
Treatment for most people with desmoplastic mesothelioma is palliative. Treatments may extend the patient’s life, but mostly reduce symptoms. If tumor size is reduced, the patient experience less pain and find breathing easier. Because desmoplastic mesothelioma causes fluid to build up between tissue layers, draining fluid also helps ease pain and discomfort.
Prognosis
The prognosis for desmoplastic mesothelioma is not usually positive. Because mesothelioma is generally difficult to diagnose (this sub-type in particular), it usually isn’t discovered until the cancer is in the later stages. At this point, it is virtually impossible to cure and life expectancy is short. Duration of survival for desmoplastic mesothelioma, is between five and seven months after diagnosis. Treatments at this point are only used for palliative care.
If you have symptoms that could indicate mesothelioma, getting a fast diagnosis is crucial. Mesothelioma is rare. However, if you have been exposed to asbestos, you may have developed this type of cancer. Regardless of the cellular sub-type, mesothelioma is difficult to treat and has poor survival rates. Receiving a diagnosis is the best thing you can do for your future and for your loved ones.
Page Medically Reviewed and Edited by Pinar Kanlikilicer, PhD
Dr. Pinar Kanlikilicer has a PhD in Biomedical Engineering. She completed her 5-years of postdoctoral training in the Department of Experimental Therapeutics at MD Anderson Cancer Center. She is currently working in the field of cancer as a research scientist.
