Biphasic Mesothelioma

Biphasic mesothelioma cancer is so named because it manifests both epithelioid and sarcomatoid mesothelioma cells.  The disease is not identified with any one cellular structure but rather with the two types of cells that between them constitute over 95% of all mesothelioma diagnoses.  Exactly how the two cellular components come together isn’t clear – it’s possible that asbestos fibers lodged in both the pleural mesothelium, and in some form of connective tissue in a location around the lungs or in the peritoneal cavity (the abdomen).

The patient with biphasic mesothelioma has disease characterized by two malignant cell types that differ in shape and size, and in patterns of behavior.  Sarcomatoid cells tend to be more active, to produce other malignant cells at a greater pace and to spread at a quicker rate than epithelioid mesothelioma cells.  Clinical tests have found certain chemotherapy drugs to be effective against one cell and ineffective against the other.  That is one reason why so many malignant mesothelioma cases are treated with chemotherapy ‘cocktails’ comprised of multiple chemo drugs and radiation therapy as well.

Over the past several years the epidemiologists tracking mesothelioma have seen a rise in the frequency of biphasic mesothelioma.  Epithelioid pleural mesothelioma – cancer of the lining around the lung – is by far the most common mesothelioma diagnosis.  However biphasic mesothelioma has risen steadily in frequency, representing a quarter of all cases twenty years ago to 45% and more today. 

There are some interesting characteristics to biphasic manifestations of this disease.  The epithelioid and sarcomatoid cells are not necessarily intermingled, but may well be grouped with like cells in separate locations within the diseased tissue.  Biphasic mesothelioma may have malignant epithelial cells in one portion of the membrane and a sarcomatoid tumor in the lung itself, or sarcomatoid cells in another portion of the mesothelium. 

The fact that mesothelioma is a diffuse cancer rather than one concentrated in tumors (sarcomas) means that a biopsy might find the malignant epithelial cells to be expected in mesothelioma and miss sarcomatoid cells located elsewhere.  One of the reasons that the incidence of biphasic mesothelioma may have risen in recent years is the practice of multiple biopsies to determine the spread of this complicated disease.

 The National Cancer Institute maintains a database of all clinical trials being conducted for cancer.  There are over 6,000 of them and there are at least two dozen that are focused solely on mesothelioma.  Many are concentrated on pleural mesothelioma but that does not preclude targeting both epithelioid and sarcomatoid cancer cells. 

In fact several of them are experimenting with using the drug pemetrexed along with other established chemotherapy drugs such as cisplatin to determine how best to choke off the growth of mesothelioma cancer cells.  Some cells are effectively destroyed by an enzyme, for example, while others are unaffected.  This suggests that the trials are taking into account the possibility of biphasic pleural mesothelioma as an important aspect of the disease to take into account during a research program.