Sarcomatoid Mesothelioma

Sarcomatoid mesothelioma is a much rarer form of the disease than epithelioid mesothelioma, comprising fifteen to twenty percent of all diagnosed cases.  The generic term sarcoma refers to cancer originating from mesodermal or connective tissues in the body – which would include fat, muscle and bone.  Sarcomatoid mesothelioma cells originate in a different fashion than epithelial cancer cells, which are derived from the cells that make up the mesothelium, the membrane lining the chest and abdominal cavities as well as the heart and the lungs.

Sarcomatoid mesothelioma is more likely to originate in the peritoneal or abdominal cavity.  The cell type is such that it is difficult to differentiate between sarcomatoid mesothelioma cells and cells of other types of sarcoma cancers found in the lungs and abdomen.  In general, sarcomatoid mesothelioma cells  show more abnormality than their epithelioid counterparts, and under diagnostic study often display mitotic activity – that is, the processing of cell splitting and reproducing.

The challenge for the physician is determining whether sarcomatoid mesothelioma cells are in fact cancer of the mesothelium or represent some other sarcoma – a more common lung tumor or even melanoma.  Sarcomatoid mesothelioma cells can easily be mistaken for sarcoma cells that are linked with not only lung tumors but organs in the peritoneal cavity. 

Identifying the true source of the cancer may be a matter of diagnosing the mass itself.  pleural mesothelioma – cancer of the membrane around the lung – is relatively diffuse, spread across the surface of the mesothelium, rather than concentrated as in a tumor mass.  Clues like this help the medical professional identify sarcomatoid mesothelioma as opposed to some other cancer.

Sarcomatoid cells will also respond to different treatment choices than epithelial mesothelioma cells.  Chemotherapy drugs that attack the proteins in an epithelioid cell may contain an enzyme that a sarcomatoid cell may resist.  Treatment of sarcomatoid mesothelioma is judged to be more difficult that epithelioid mesothelioma – in part, perhaps, because cases of pure sarcomatoid mesothelioma are so rare.  

It is also true, however, that sarcomatoid cells are more aggressive than the more common epithelioid cells.  The cancer moves more rapidly and the prognosis is therefore somewhat poorer than for a patient with the more common mesothelioma variety, which originates in the pleural mesothelium around the lungs and attached to the chest wall.

It is more common to find sarcomatoid cells joined in combination with epithelioid mesothelioma cells in some fashion.  This form of the disease is called biphasic mesothelioma, and has grown over the last decade from twenty five percent of all mesothelioma diagnoses to a figure now approaching forty percent.