There are three cellular variations for mesothelioma; the most common form of the disease is generated by epithelial cells, while sarcomatoid mesothelioma is rarer - occurring in about 20% of all cases. The third variation is biphasic mesothelioma, which is composed of both epithelioid and sarcomatoid cell types. Sarcomatoid mesothelioma is more difficult to treat than the more common form of the disease, for a variety of reasons.
Sarcomatoid cells are known as spindle cells because of their physical characteristics. One of the issues that diagnosing physicians confront is trying to differentiate between sarcomatoid mesothelioma and a couple of other forms of cancer that mimic it: true, high grade sarcoma and pulmonary sarcomatoid carcinoma. Determining the difference is critical for purposes of selecting treatment options.
Diagnostic Methods for Sarcomatoid Mesothelioma
It takes more than inspection with a microscope to determine if a sarcomatoid malignancy is in fact mesothelioma. Tests involving the use of various types of protein cells to observe that bind with the malignant cell in question are used to pinpoint the type of cancer represented by the malignancy. This process is called Immunohistochemistry, the study of molecular markers by using antibodies to test their reaction. Many of the protein markers used in these tests respond in similar fashion to sarcomatoid mesothelioma and other forms of sarcomatoid carcinoma, particularly in the pleural region - where the most common form of mesothelioma develops. Pleural mesothelioma is found in the lining around the lungs.
Certain proteins or antibodies will interact with a malignant cell in such a manner as to produce a coloring reaction in the cell. This reaction is called "staining" and has become a standard method of cell identification. The key to this process is utilizing antibodies that do not create the same coloring response in malignant cells that mimic those of sarcomatoid mesothelioma.
Tumor Types in Sarcomatoid Mesothelioma
The nature of the tumors generated by mesothelioma can be another clue to diagnosis of this particular form of cancer. Mesothelioma displays as a "diffuse" form of the disease, meaning it is characterized by a series of malignant nodes spread over an area of tissue. Other types of cancer generally are in the form of a principal tumor or mass, a single large entity that looks very different when viewed by a MRI scan or some other imaging technique.
If a sarcomatoid mesothelioma patient is diagnosed early enough to allow for surgical intervention, the resection process involves removal of as much of the tissue that the cancer has spread over as possible. For pleural mesothelioma patients this means removal of the tissue around the lungs; for those with abdominal or peritoneal mesothelioma it means removal of the lining on the abdominal wall. However sarcomatoid mesothelioma may also develop as a single tumor.
1. Sarcomatoid mesothelioma and its histological mimics: a comparative immunohistochemical study. Lucas et al, Histopathology, March 2003
2. Differential diagnosis of sarcomatoid mesothelioma from true sarcoma and sarcomatoid carcinoma using Immunohistochemistry. Kushitani et al, Pathology International, February 2008
3. Peritoneal Mesothelioma, Ros et al, Acta Radiologica, January 1991
