Key Takeaways
- Epithelioid mesothelioma is the most common subtype of mesothelioma, accounting for 50–70% of all cases. It originates in epithelioid cells — the cells that line the surfaces of organs, most commonly in the pleural tissue around the lungs.
- Epithelioid mesothelioma has the best prognosis of the three subtypes because it grows more slowly, forms characteristic clusters that are easier to diagnose, and adheres to healthy tissue less aggressively than sarcomatoid or biphasic forms.
- Epithelioid tumors have a distinct circular shape with large, visible nuclei. The cells group in recognizable clusters, making them easier for pathologists to identify under microscopy.
- Treatment typically involves a multimodal approach — combining surgery (when possible) with chemotherapy and/or clinical trial therapies.
- The World Health Organization has updated its diagnostic framework beyond the traditional three-subtype classification. Doctors are increasingly using immunohistological indicators — including biomarkers, immune checkpoints, and blood-based markers like calretinin (a calcium-binding protein present in almost every epithelioid case) — to diagnose this subtype faster and more accurately.
What are Epithelioid Cells?
Epithelioid cells line the surfaces of organs; most commonly, these cells are associated with the
outermost layer of the skin, the epidermis. Epithelioid cells have a marked physiology: they have
large, visible nuclei, often arrange themselves in distinct shapes, and divide relatively faster than
other types of somatic cells. They are categorized based on their shape, which can be columnar,
cubed, or flat (squamous).
How is Epithelioid Mesothelioma Different From Other Forms of Mesothelioma?
This subtype of mesothelioma is the most common form of mesothelioma. By “form,” we mean how
and where the aggressive cancer originates. Like the other manifestations of mesothelioma,
epithelioid is known to be associated with asbestos exposure.
● About 50-70% of all mesothelioma cases originate in the epithelial pleural tissues around
the lungs.
● Epithelioid mesothelioma tumors–despite the epithelial tendency to quickly divide–grow
more slowly than other types of mesotheliomas.
● Epithelioid mesothelioma tumors have a distinct circular shape. The cancerous cells
group in characteristic clusters, which makes them somewhat easier to diagnose
compared to biphasic or sarcomatoid originations. (Biphasic and sarcomatoid refer to the
types of cells that mesothelioma can originate in, just like “epithelioid” refers to a class of
cells.)
● The prognosis for epithelioid mesothelioma is relatively better than the rarer originations;
this is because a.) it is easier to diagnose; b.) more is known about its growth and
progression; and c.) its characteristic clusters adhere to and impact healthy tissue more
slowly.
● Multimodal treatment, or using different therapies in conjunction with one another, is
usually the best course of action of epithelioid mesothelioma. Usually, these treatments
include surgery (if possible) and either chemotherapy or a clinical trial.
The Nuclear Grading Scale
Although we had covered the three distinctions of mesothelioma cell type, the World Health
Organization (WHO) recently revamped the diagnostic and phenotypic (how it physically looks
and is situated) requirements for mesotheliomas. The breaking down of mesotheliomas into three
subtypes is called nuclear grading. While this is important for distinguishing possible treatment
options and prognostic outcomes, it’s relatively fallible and inexact. Instead, doctors are opting
for immunohistological indicators of epithelioid mesothelioma. This means that they’re looking
for certain biomarkers and immune checkpoints that align with previous epithelioid
mesothelioma cases. For instance, a certain immune cell might be significantly upregulated, or
there could be certain mutations in the tumor’s cells that are characteristic of epithelioid
mesothelioma. There are also blood-based markers of epithelioid mesothelioma: calretinin is a
calcium-binding protein that is present in almost every case, and its presence can be tested for
within a few minutes.
New diagnostic criteria are helping doctors more quickly identify epithelioid mesothelioma and
the other subtypes of mesothelioma, too. This means that treatment plans can be administered
much more quickly than in the past. Because we’ve established that mesothelioma is an
aggressive cancer, the sooner the diagnosis, the better the prognosis. As diagnostic criteria
evolve, so will the prognosis for mesothelioma.
If you or a loved one has been diagnosed with an asbestos-related disease, please call
(800)-505-6000 for legal help. For more information, fill out the form on our Contact Us page.
Frequently Asked Questions
What is epithelioid mesothelioma?
Epithelioid mesothelioma is the most common subtype of mesothelioma, accounting for 50–70% of all cases. It originates in epithelioid cells — the cells that line the surfaces of organs throughout the body. In mesothelioma, it most commonly develops in the pleural tissue surrounding the lungs. Like all forms of mesothelioma, it is caused by asbestos exposure.
What are epithelioid cells?
Epithelioid cells line the surfaces of organs throughout the body — the most commonly known example is the epidermis (the outermost layer of skin). These cells have large, visible nuclei, arrange themselves in distinct shapes, and divide relatively quickly compared to other cell types. They are categorized by shape: columnar, cubed, or flat (squamous). When these cells become cancerous due to asbestos exposure, they form the epithelioid subtype of mesothelioma.
Why does epithelioid mesothelioma have a better prognosis than other subtypes?
Epithelioid mesothelioma generally has the best prognosis of the three subtypes for several reasons:
- Slower growth — despite epithelial cells’ tendency to divide quickly, epithelioid mesothelioma tumors grow more slowly than sarcomatoid or biphasic forms
- Easier to diagnose — the tumors form distinct circular shapes and characteristic cell clusters that pathologists can identify more readily
- Less aggressive spread — epithelioid tumors adhere to and impact healthy tissue more slowly than other subtypes
- More research — because it’s the most common subtype, more is known about its growth patterns, progression, and effective treatments
How is epithelioid mesothelioma diagnosed?
Traditionally, mesothelioma has been classified into three subtypes through a process called nuclear grading — examining the cells under a microscope to determine whether they are epithelioid, sarcomatoid, or biphasic. However, doctors are increasingly moving beyond this three-category system and using more advanced methods:
- Immunohistological indicators — looking for specific biomarkers and immune checkpoints that are characteristic of epithelioid mesothelioma
- Genetic markers — identifying specific mutations in the tumor’s cells
- Blood-based markers — testing for calretinin, a calcium-binding protein present in almost every epithelioid mesothelioma case, which can be detected within minutes
These newer diagnostic criteria help doctors identify epithelioid mesothelioma faster and begin treatment sooner.
What is calretinin and why is it important?
Calretinin is a calcium-binding protein that is present in nearly every case of epithelioid mesothelioma. It can be detected through a simple blood test within a matter of minutes, making it one of the fastest and most reliable biomarkers for this subtype. Its presence helps doctors distinguish epithelioid mesothelioma from other cancers that may look similar under a microscope — accelerating the diagnostic process and allowing treatment to begin sooner.
How is epithelioid mesothelioma treated?
Treatment for epithelioid mesothelioma typically involves a multimodal approach — combining two or more therapies. The most common combination includes:
- Surgery — when the tumor is resectable, surgical removal is usually the first step
- Chemotherapy — often used before or after surgery to shrink tumors or target remaining cancer cells
- Clinical trials — newer therapies including immunotherapy, vaccine-based treatments, and epigenetic approaches may be available for eligible patients
Because epithelioid mesothelioma grows more slowly and responds better to treatment than other subtypes, patients often have a wider range of treatment options available to them.
What are the other subtypes of mesothelioma?
In addition to epithelioid, there are two other mesothelioma cell subtypes:
- Sarcomatoid — the most aggressive subtype, accounting for 10–20% of cases. It tends to grow faster and is harder to treat.
- Biphasic — contains both epithelioid and sarcomatoid cells, accounting for 20–30% of cases. Prognosis depends on which cell type is more dominant in the tumor.
Correctly identifying the subtype through biopsy and advanced diagnostics is critical because it directly affects treatment decisions and expected outcomes.
What should I do if I’ve been diagnosed with epithelioid mesothelioma?
If you or a loved one has been diagnosed with epithelioid mesothelioma or another asbestos-related disease, understanding your treatment options and legal rights is an important first step. Because epithelioid has the best prognosis of the three subtypes, early and aggressive treatment can make a meaningful difference. Call (800) 505-6000 or fill out our contact form for a free consultation.
