Written By: Devin Golden

Sarcomatoid Mesothelioma Diagnosis

Sarcomatoid mesothelioma is the rarest of the mesothelioma cell types. This diagnosis is made when a patient is found to have sarcomatoid cancer cells in their tumor tissue. The only way to diagnose mesothelioma is through a tissue biopsy.

Karen Ritter, RN BSN

Medically Reviewed By

Karen Ritter, RN BSN

Registered Nurse

Karen Ritter, RN BSN

Medically Reviewed By

Karen Ritter, RN BSN

Registered Nurse


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Important Facts About Diagnosing Sarcomatoid Mesothelioma

  • Sarcomatoid mesothelioma is diagnosed by analyzing tissue under a microscope to examine the appearance of the cells and the presence of any cancerous proteins in the cells.
  • The medical professionals examining the tissue samples under the microscope are called pathologists. They use a cell staining process to determine if cancerous proteins are present.
  • Following a diagnosis of sarcomatoid mesothelioma, doctors will determine the stage of the cancer based on how far the disease has spread.

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:

  1. Patient meets with a doctor after experiencing symptoms
  2. Patient undergoes imaging tests, such as an X-ray, CT scan or MRI scan
  3. If these tests show signs of mesothelioma – such as an unexplained mass or thickening within the thoracic cavity or abdomen – the doctor will recommend a biopsy to remove tissue from the area of abnormality
  4. After the patient undergoes a tissue biopsy, doctors send the tissue samples to a laboratory for a pathologist to review under a microscope
  5. If mesothelioma cells are present, pathologists will determine the cell type (epithelioid, sarcomatoid, or biphasic)

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

Frequently Asked Questions About Diagnosing Sarcomatoid Mesothelioma

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How is Sarcomatoid Mesothelioma Diagnosed?

Sarcomatoid mesothelioma is diagnosed by doctors removing tissue from the patient and sending it to a laboratory for examination. Pathologists study the tissue under a microscope for signs of mesothelioma, such as the physical appearance of the cells and whether they express any cancerous proteins linked to sarcomatoid mesothelioma.

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Can Sarcomatoid Mesothelioma Be Diagnosed Without a Biopsy?

No, the only way to definitely determine if a patient has sarcomatoid mesothelioma or any other cell type of this cancer is through a tissue biopsy. Some doctors may be able to obtain a mesothelioma diagnosis with a fluid sample, but a tissue sample is more conclusive.

Sources & Author

  1. Sarcomatoid mesothelioma: a clinical-pathological correlation of 326 cases. Modern Pathology. Retrieved from: https://www.nature.com/articles/modpathol2009180.pdf. Accessed: 09/04/18.
  2. Guidelines for Pathologic Diagnosis of Malignant Mesothelioma. Archives of Pathology and Laboratory Medicine. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/28686500/. Accessed: 10/04/19.
  3. Immunohistochemistry. National Cancer Institute. Retrieved from: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/immunohistochemistry. Accessed: 10/04/19.
  4. Malignant Mesothelioma Stages. American Cancer Society. Retrieved from: https://www.cancer.org/cancer/types/malignant-mesothelioma/detection-diagnosis-staging/staging.html. Accessed: 05/04/2023.
Devin Golden

About the Writer, Devin Golden

Devin Golden is a content writer for Mesothelioma Guide. He produces mesothelioma-related content on various mediums, including the Mesothelioma Guide website and social media channels. Devin's objective is to translate complex information regarding mesothelioma into informative, easily absorbable content to help patients and their loved ones.