Sarcomatoid Mesothelioma Diagnosis

How is Sarcomatoid Mesothelioma Diagnosed?

Sarcomatoid mesothelioma is diagnosed by examining cells from a tissue biopsy. Surgeons perform a surgical biopsy by removing a sample of tissue from the chest or abdominal cavity and examining it under a microscope. Pathologists will determine if sarcomatoid mesothelioma cells are present through a process of sectioning, staining and examining the microscopic structures of the tissue.

There are three mesothelioma cell types: epithelioid; sarcomatoid; and biphasic. The last is a combination of epithelioid cells and sarcomatoid cells.

Sarcomatoid mesothelioma is the least common cell type of this cancer. Approximately 10%-20% of diagnosed cases are classified as sarcomatoid mesothelioma.

How to Determine the Mesothelioma Cell Type

The science of identifying the mesothelioma cell type is called pathology, which is the microscopic study of tissue or fluid samples for the presence of cancer. Through pathology tests, which are conducted in a laboratory, doctors create a pathology report to summarize the findings and specify what mesothelioma cell types are present – if any.

These scientific tests are conducted by pathologists, who examine the appearance of cells and how they react to staining. The staining process is how pathologists can determine if the cells contain cancerous proteins, which is the definitive way to diagnose cancers such as mesothelioma.

Pathologists identify the cell type based on the cells’:

• Behavior
• Size and shape
• Nuclei
• Pattern of the sample

Staining for Sarcomatoid Mesothelioma Cell Proteins

Diagnosing sarcomatoid mesothelioma begins with extracting tissue or fluid samples to collect cells. Doctors usually prefer tissue samples as they are more likely to contain enough cells for accurate testing.

The samples are then sent to a laboratory for immunohistochemistry staining, which is performed by a pathologist. They stain, or dye, cells to help identify antibodies and proteins unique to the cancer. When antibodies are added to the tissue sample, they will find and bind to the antigens found on sarcomatoid mesothelioma cells (like a key into a lock), and the stain is activated.

When staining tissue or fluid samples, pathologists look for the following proteins as signs of sarcomatoid mesothelioma:

• Podoplanin (D2-40)
• Pancytokeratin
• Calretinin
• GLUT1

What Do Sarcomatoid Mesothelioma Cells Look Like?

Sarcomatoid mesothelioma cells have an appearance that can be difficult to identify among healthy tissue. The cells can also look different from one another.

Sarcomatoid cells are long, narrow and shaped like ovals. They also have enlarged, elongated nuclei and could even have more than one nucleus.

Steps of a Sarcomatoid Mesothelioma Diagnosis

There are important steps that are followed to determine a mesothelioma diagnosis. These steps do not change regardless of the cell type.

The steps to determine a sarcomatoid mesothelioma diagnosis are:

Stages of Sarcomtoid Mesothelioma

After receiving a diagnosis of sarcomatoid mesothelioma, patients will likely learn the stage of their cancer. Most types of cancer have four stages – stage 1, stage 2, stage 3, and stage 4 – with each stage associated with a more advanced disease. Doctors can determine the stage of mesothelioma by performing additional testing for evidence of cancerous cells throughout the body and the size of tumors.

Determining the Stage of Sarcomatoid Pleural Mesothelioma

There are four stages of sarcomatoid pleural mesothelioma:

• Stage 1 – The earliest stage, defined by tumors localized to the pleura, which is the thin lining of the lungs where pleural mesothelioma begins (D2-40)
• Stage 2 – Characterized by tumors found in the pleura on one side of the chest with possible tumor spread into the diaphragm or lung tissue on the same side
• Stage 3 – Tumors have spread past the pleura and to the nearby lung, into the chest wall, to the diaphragm, and to the mediastinum (the space between your lungs)
• Stage 4 – The most advanced stage, defined by tumors spread throughout the thoracic cavity and into other areas of the body (abdominal cavity, spinal cord or brain)

Determining the Stage of Sarcomatoid Peritoneal Mesothelioma

Doctors determine the stage of sarcomatoid peritoneal mesothelioma with the peritoneal cancer index (PCI), which measures how much cancer is in the abdominal cavity. The abdomen is divided into 13 sections, and each section of the abdominal cavity receives a score of 0-3 depending on the extent of disease in each section. The scores of each section are added up to determine the stage of peritoneal mesothelioma.

Doctors associate a patient’s PCI score with one of the four stages used for most types of cancer: 

• Stage 1 –  PCI score between 1 and 10
• Stage 2 – PCI score between 11 and 20
• Stage 3 – PCI score between 21 and 30
• Stage 4 – PCI score between 31 and higher