Mesothelioma Cell Types

There are three major cell types found in malignant mesothelioma: epithelioid, sarcomatoid, and biphasic.

The original mutated cell can be one of these three types and is caused when the cell is exposed to asbestos. Epithelial mesothelioma is the most commonplace of the three, being responsible for more than half of all total mesothelioma cases. Each case tends to be highly unique and the treatment plan and corresponding prognosis are significantly affected by the cell type.

What Are The Types Of Cells

Mesothelioma tumors are classified by the shape and characteristics of the cells that comprise them. The primary mesothelioma cell types are epithelioid, sarcomatoid, biphasic.

The cells are classified both by their appearance under magnification, but also how they behave and grow to form the tumors.

There are several subtypes, but they are rare. They are subtypes of the other primary cell types and are generally considered rare histological variances. Besides the cell type, mesothelioma is classified by the location of the main tumor. The four different types are testicular, peritoneal, pericardial, and pleural.

Testicular mesothelioma is the rarest form and occurs in the lining of the testes. Peritoneal mesothelioma is a tumor in the abdominal cavity, usually near the pelvis. Pericardial mesothelioma is a tumor that grows in the tissue that lines the heart sac. Pleural mesothelioma is the most common form and features a cancerous tumor that grows on the mesothelial cells of the pleural space in the chest cavity. Oncologists can determine important details about a tumor by studying the cell type and tumor location. 

Each type of mesothelioma cell responds to treatments in various ways. Both the location and the mesothelioma cell type will have a significant effect on each patient’s prognosis. Once there has been a positive diagnosis, the patient’s doctor will begin to study the mesothelioma pathology to determine possible treatment plans and prognosis.

What Is Histology?

Mesothelioma histology is the study of the physical features of the cancerous cells in the mesothelial tissue.

Histology is a type of biological analysis that is centered around the study of individual cells and various tissues. Histopathology is focused on the study of diseased or damaged cells and is a type of pathology.

A pathologist will use a variety of histologic methods to obtain the most accurate information about the patient’s mesothelioma cell type or subtype. A histologic analysis will utilize a microscope to view cells under powerful magnification. Sometimes dyes or stains will be used to give better contrast and enable more confident identification or diagnosis.

There is significant training required to become specialized in cancer cell identification. Often pathologists will pursue that additional specialization in cancer identification and a small number of those may specialize even further and focus on mesothelioma cells exclusively.

Histologic confirmation helps minimize misdiagnosis of mesothelioma in someone who does not have it. For example, the cells of ovarian cancer are incredibly similar to the cells of mesothelioma and only a deep histologic investigation would be able to tell with any confidence one from the other. Similar difficulty in identification can occur between small cell lung cancer and pleural mesothelioma. 

Cell Types

When tissue samples have been collected and the pathologist is determining what type of mesothelioma is present, they are looking for the three different cell types: epithelial, sarcomatoid, or biphasic.

Epithelial Cells

Epithelial cells are even and uniform in appearance and will be square, round, or polygonal in shape and configuration. When viewed with a microscope they have obvious, dark nuclei and while they divide quickly, they tend to spread slowly. The slow spread is due to the adhering primarily to themselves in most cases. Mesothelioma tumors with epithelial cells account for between 50% and 70% of all cases diagnosed. Treatment for epithelial cell mesothelioma tends to be more effective than for other types, often leading to a more positive prognosis.

Sarcomatoid Cells

The spindle-shaped sarcomatoid cells do not seem to have a rigidly defined structure and are configured in irregular patterns. They can spread quicker and easier than epithelioid cells because they don’t stick to each other as much as the epithelioid cells do. Sarcomatoid mesothelioma is relatively rare and accounts for approximately 10% to 20% of total cases. Treatment options are more limited usually since it is often not diagnosed until a more advanced stage. Due to the irregular structure and sometimes widespread nature of this type of mesothelioma, surgery is often ineffective.

Biphasic Cells

Some mesothelioma tumors have both epithelioid and sarcomatoid cells and they are known as biphasic tumors. They contain various ratios of both of the other main cell types and account for approximately 20% to 30% of total mesothelioma diagnoses. Treatment effectiveness and prognosis are often highly dependent on the ratio of epithelioid cells to sarcomatoid cells. Prognosis is often better if there is a higher proportion of epithelial cells since they are easier to treat. Treatment plans may often feature several various treatments, such as chemotherapy, surgery, and radiation.

Rare Mesothelioma Variants


This is a variant of epithelial mesothelioma and the cells create small structures that resemble glands. Also known as glandular or microglandular mesothelioma. 


Extremely rare subtype of mesothelioma that is neither the result of exposure to asbestos fibers nor is it cancerous. Continued relapses can begin to express malignancy.


This epithelial subtype creates round cysts that are connected with fibrous tissue. 

Small Cell

This is a subtype where the tumor is composed of cells that are smaller and patterned similarly to small-cell carcinoma, a lung cancer. This type can complicate the diagnosis of either mesothelioma or small-cell lung cancer.


Another variant of epithelial mesothelioma closely mimics healthy cells and even has a greatly reduced growth and division rate. It does not generally spread to other tissues, organs, or systems. 


An extremely rare variant where the tumors have tissues different from where they are located. These are rare enough that only a handful of cases have ever been documented in the medical literature.