Biphasic mesothelioma consists of both epithelioid and sarcomatoid mesothelioma cells. The World Health Organization’s (WHO) guideline for diagnosing mesothelioma as biphasic is that there are at least 10 percent epithelioid cells and 10 percent sarcomatoid cells present in the tissue sample. However, no clinical data exists that supports this guideline, so it remains controversial.
This mesothelioma cell type accounts for approximately 30 percent of all mesotheliomas. It occurs more frequently in patients with pleural mesothelioma than in those with peritoneal mesothelioma.
The cell patterns are the same as the cell patterns for each of the individual component cells (see epithelioid histopathology and sarcomatoid histopathology). However, biphasic mesothelioma may contain 50 percent less of the dense, fibrous structures that connect cells than the other mesothelioma cell types do. This is important because it can make the disease appear to be benign, which could cause it to be confused with the reactive tissue of cells called pleural fibroblasts that are released by the immune system in response to cell injury.
One of the ways that biphasic mesothelioma is diagnosed is through biopsy. However, it may not always be the most accurate method. In a study published March 2011 in the Journal of Thoracic Oncology, researchers examined the accuracy of classifying mesothelioma cell subtypes based on diagnostic biopsies.
They reviewed the records of 83 patients who underwent an extrapleural pneumonectomy from 1994 to 2009. They also examined the patients’ specimens that were taken during the procedure, which had been archived. The researchers compared the cell subtype in each patient’s record against their findings when they determined cell subtype based on the physical specimen.
The original determination about cell subtype that was in each patient’s record was based on samples obtained through different procedures. What the researchers found was that the diagnosis of biphasic mesothelioma was correct only 26 percent of the time because of errors that were made when the samples were taken. They also found that the most accurate samples were taken when the biopsy was performed during a thoracotomy. This is a procedure in which an incision is made in the chest that allows the surgeon to have access to the organs within the chest.
Immunohistochemistry Can Help Accurately Diagnose Biphasic Mesothelioma
Immunohistochemistry is procedure that looks for markers that signal the presence of a specific disease. It is based on the principal that the immune system sends out a particular protein, called an antibody to attack a specific foreign body or antigen. A tissue sample is stained with special dyes. When the sample is viewed under an electron microscope, if the proteins that bind to mesothelioma cells are there, the pathologist can confirm any earlier diagnosis that was made based on a biopsy specimen about the presence of the disease and what cell subtype it is.
The marker that appears to be most conclusive in diagnosing biphasic mesothelioma is D2-40. It is highly responsive to the membranes of epithelioid cells and to the material within sarcomatoid cells.