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What Are the Different Types of Mesothelioma Cells?

There are three major mesothelioma cell types.

  • Epithelioid
  • Sarcomatoid
  • Biphasic

These cell types differ based on how they look under a microscope and how they grow and form cancerous tumors in the body.

There are numerous, rare cellular subtypes within and along with each of the three main mesothelioma cell categories. These are considered rare variances in histological mesothelioma types.

In addition to cell type, the type of mesothelioma is designated by the location of the tumor. The four types of mesothelioma defined by tumor location are pleural, peritoneal, pericardial and testicular.

Pleural mesothelioma occurs in the chest cavity lining. Peritoneal disease is found in the lining of the abdominal cavity. Pericardial tumors form in the lining around the heart, and testicular mesothelioma occurs in the lining around the testes.

Using tumor location and mesothelioma cell type, doctors can designate key details about a patient’s tumor. For example, a person can have a peritoneal tumor of epithelial cell type or a pleural cancer composed of sarcomatoid cells.

Facts About Mesothelioma Cells

  • Tumors are classified into three main cell types.
  • Epithelial cells are more common and easier to treat.
  • Sarcomatoid cells are rare and harder to treat.
  • Doctors identify the cell type by studying tissue samples of the cancer.

Each cell type responds to treatment differently and affects the individual patient’s prognosis. Once you receive a definitive mesothelioma diagnosis, your doctor will study your cancer pathology report to understand all of the details of your mesothelioma cell type.

This information is critical and accurate mesothelioma testing of the cell type is essential to developing an effective treatment plan.

Recent international guidelines from a 2021 research study suggest the use of an advanced microscopic technique called electron microscopy when further support of a diagnosis of mesothelioma is needed. 

What Is Mesothelioma Histology?

Mesothelioma histology involves the study of cancerous mesothelial cells.

Histology is a branch of biology that involves the study of cells and tissues. Histopathology is the study of diseased cells. Histopathology falls within the larger field of pathology.

Your pathologist will use histology techniques to provide the most accurate information about your mesothelioma cell type.

Histology technicians use microscopes to view cells up close. They prepare samples of tissue with chemical stains. The stains make the cells’ features stand out to help with identification.

It takes special training to identify cancer cells. Board-certified pathologists often become specialized in identifying different types of cancer. A small number of pathologists specialize in identifying mesothelioma cells.

Histology also helps prevent mesothelioma misdiagnosis. For example, peritoneal mesothelioma and ovarian cancer can be difficult to differentiate. Analyzing the cell type helps doctors tell the difference.

Sometimes doctors struggle to tell the difference between pleural mesothelioma and lung cancer. In a 2019 case report, a patient appeared to have lung cancer, but proper pathology testing revealed mesothelioma cancer cells, not lung cancer cells.

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Cell Types of Malignant Mesothelioma

Pathologists look for three different types of cells — epithelial, sarcomatoid and biphasic — within tissue samples when mesothelioma is suspected.

Epithelial Cells

These mesothelioma cells are uniform, sharply defined and square to tubular in configuration. They feature prominent nuclei and divide quickly but tend to stick together. This means it takes longer for them to spread throughout the body. The epithelial cell type accounts for more than 50% of all mesothelioma cases and up to 70% of cases.

Treatment: Epithelial cell mesothelioma typically is the most responsive to treatment. This can lead to a better prognosis.

Sarcomatoid Cells

Spindle-shaped sarcomatoid cells typically lack defining structure and have an irregular configuration. They spread more quickly than epithelial cells because they don’t tend to stick together as they grow. This rare cell type characterizes 10% to 20% of cases.

Treatment: Because sarcomatoid cell mesothelioma is more aggressive and more likely to be diagnosed at an advanced stage than epithelial type, this cancer often has fewer treatment options. It forms less clear-cut tumor boundaries and is harder to treat surgically.

Biphasic Cells

Malignant mesothelioma is considered biphasic when it contains epithelial and sarcomatoid cells. Each cell type must account for at least 10% of the tumor mass to receive a biphasic diagnosis. The biphasic (mixed) cell type accounts for 20% to 30% of mesothelioma cases.

Treatment: Treatment options are better and life expectancy is longer if there are more epithelial cells and fewer sarcomatoid cells. Treatment options can include surgery, chemotherapy and radiation.

Each cell type has different visible characteristics when examined under a microscope. For example, sarcomatoid cells have elongated nuclei. Epithelial cells have microvilli (microscopic protrusions of the cell) and clear structures called organelles within each cell.

Doctors use these histological classifications to confirm the diagnosis. Along with staging information, they can use this information to estimate prognosis and develop a treatment plan.

Each cell type responds differently to treatment.

  • Epithelial cells typically are the most responsive to treatment, which often leads to a better prognosis.
  • Sarcomatoid cells are the least responsive to treatment. Some mesothelioma specialists do not consider sarcomatoid tumors eligible for surgical removal.
  • Biphasic cell type contains some sarcomatoid cells and also may be considered less treatment responsive than epithelial cell type. The exact prognosis depends on the ratio of epithelial to sarcomatoid cells. More epithelial and fewer sarcomatoid is associated with a better prognosis.

The appearance of the different cell types is subtle. This fact can make the diagnostic process quite challenging. For example, distinguishing mesothelioma cells from adenocarcinoma cells can be a serious challenge. Only the most experienced mesothelioma pathologists can easily tell the difference.

Rare Variances in Histological Mesothelioma Types

Some rare mesothelioma cells can be histologically classified with more detail than the three major cell classifications of epithelial, sarcomatoid and biphasic.


In this variant of epithelial mesothelioma the cells line small, gland-like structures. This type is also called glandular or microglandular mesothelioma.


Benign mesothelioma is neither cancerous nor the result of asbestos exposure.


This type has smooth, thin-walled cysts held together by fragile fibrovascular tissue. It is a subtype of epithelial mesothelioma.


The term deciduoid reflects this unusual epithelial cell subtype’s histological resemblance to cell changes occurring in early pregnancy. It most commonly affects young women.


In this form of sarcomatoid mesothelioma, more than 50% of the tumor is made of dense, fibrous tissue.


Tumors of heterologous cell type contain bodily tissues different from the tissues in which they form. Only a handful of cases are documented in the medical literature.


This subtype of sarcomatoid mesothelioma is often misdiagnosed. It is made up of a dense bundle of inflammatory and immune cells.


This variant of epithelial mesothelioma resembles healthy cells that grow and multiply at a slow rate. It does not typically spread to other parts of the body.

Small Cell

This type occurs when a large proportion of a mesothelioma tumor is made up of small cells that grow in a pattern similar to small-cell carcinoma.

The Histology Process

It takes a team to diagnose mesothelioma. The team includes surgeons, histotechnicians, histopathologists, pathologists and other medical professionals. They work together to provide your primary oncologist with as much information as possible about the mesothelioma cells.

Histology Process

Histology Steps to Determine Mesothelioma Cell Type

A surgeon removes tumor tissue during a biopsy or surgery and sends it to the lab. A histotechnician preserves and stains the sample with a number of special chemicals to reveal the microscopic appearance of the cells.

After fixing, embedding, sectioning, mounting the cells on slides and staining them, the histotechnician works closely with a pathologist to identify the cancer cell type or types.

Quick Fact:
“Frozen section fixation” is used to diagnose cancer during surgery. Small sections of the tumor are removed and quickly frozen while the patient is still in surgery. A slice of the frozen tissue is then stained and placed on a slide for a rapid assessment by a pathologist to determine if a tumor is malignant.

After the cancerous tissue is mounted and stained on a slide, the sample is now ready to view under a microscope. The pathologist and histotechnician note the size, shape and anatomical structure of the cells to identify the tumor’s cell type.

Additional Lab Processes to Support Histology Cell Studies

Pathologists use other techniques to learn more about cells. These techniques include in situ hybridization and immunohistochemistry.

In situ hybridization

In situ hybridization uses fluorescent or radioactive probes to bind DNA and RNA. Using this method, scientists can analyze the genes of a cell. They can also detect genetic abnormalities.


Immunohistochemistry is based on the principle that antibodies bind to specific antigens. Antibodies also bind to cancer cell proteins called oncoproteins.

Different antibodies are applied to tissues on a microscope slide depending on what type of cancer is suspected. Visual patterns are created by the interaction of antibodies and oncoproteins. These patterns help pathologists diagnose mesothelioma.

Common Immunohistochemical Markers for Mesothelioma

  • Cytokeratin 5 and 6
  • Calretinin
  • WT-1 protein
  • Podoplanin (D2-40)

Immunohistochemistry is regularly used in conjunction with other diagnostic procedures, including mesothelioma histology, to provide the most accurate the diagnosis of mesothelioma.

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