The short answer
Mesothelioma is grouped by where it starts — pleural (chest lining, most common), peritoneal (abdominal lining), pericardial (heart lining, rare), or testicular (very rare) — and by cell type: epithelioid, sarcomatoid, or biphasic. Epithelioid cell type generally has a better outlook than the others.
Pleural mesothelioma, in the lining around the lungs, is by far the most common type, making up more than 8 in 10 cases.
Peritoneal mesothelioma, in the lining of the abdomen, accounts for most remaining cases.
Pericardial (heart lining) and testicular mesothelioma are both very rare.
Mesothelioma is also classified by cell type under the microscope: epithelioid (about 6 in 10 cases), sarcomatoid, and biphasic (a mix of both).
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The full explanation.
The simple version
Mesothelioma is described in two ways at once. One is where it starts in the body. The other is how the cells look under a microscope. Both matter when you are trying to understand a diagnosis.
Types by location
- Pleural mesothelioma starts in the pleura, the lining around the lungs. It is by far the most common type. It makes up more than 8 in 10 cases.
- Peritoneal mesothelioma starts in the peritoneum, the lining of the belly. It accounts for most of the rest.
- Pericardial mesothelioma starts in the lining around the heart. This is rare.
- Testicular mesothelioma starts in the lining around the testicle. It is very rare.
Types by cell type
Under the microscope, mesothelioma cells fall into one of three main patterns.
- Epithelioid is the most common cell type. It accounts for about 6 in 10 cases. It generally has a better outlook than the other two.
- Sarcomatoid is made of spindle-shaped cells. It is the least common of the three and tends to behave more aggressively.
- Biphasic (mixed) has both epithelioid and sarcomatoid cells in the same tumor.
Why type matters
Both location and cell type affect how mesothelioma is treated. Pleural and peritoneal disease are staged and treated in different ways. People with epithelioid disease tend to have a better outlook than people with sarcomatoid or biphasic disease. Mesothelioma is rare. So it helps to have the location and cell type confirmed by a pathologist who knows it well. A second opinion is sometimes worth getting before treatment is decided.
When to get help sooner
- Call 911 or go to an emergency department if you are struggling to breathe, your breathlessness gets suddenly worse, you have severe chest pain, or one leg becomes swollen, red, and painful. Mesothelioma can cause blood clots, and fluid can build up fast around the lung.
- Call your doctor immediately if you run a temperature of 100.4°F (38°C) or higher while chemotherapy is under way. In CDC's guidance for people on cancer treatment, that fever is a medical emergency and the instruction is to phone your doctor straight away.
- Call your care team the same day if your breathing is getting worse over a few days, a fever appears when you are not on treatment, or your belly is swelling quickly or becoming painful.
- Call your care team within a day or two if you have a new cough, pain in the side of the chest or lower back, trouble swallowing, hoarseness, nausea and vomiting, or weight loss you cannot explain.
Sources
- American Cancer Society — Mesothelioma
- American Cancer Society — Signs and Symptoms of Mesothelioma
- National Cancer Institute — Malignant Mesothelioma Treatment (PDQ®) Health Professional Version
- CDC — Watch Out for Fever (Preventing Infections in People With Cancer)
- CDC — Incidence of Malignant Mesothelioma, U.S. Cancer Statistics
Words to know
Tap any term to see what it means.
Common questions
What is the most common type of mesothelioma?
Pleural mesothelioma, which starts in the lining around the lungs (the pleura), is by far the most common type, accounting for more than 8 out of 10 cases.
What is peritoneal mesothelioma?
Peritoneal mesothelioma starts in the peritoneum, the lining of the abdominal cavity. It is the second most common type and accounts for most of the remaining cases.
Are pericardial and testicular mesothelioma common?
No, both are very rare. Pericardial mesothelioma starts in the lining around the heart, and testicular mesothelioma starts in the lining around the testicle.
What do epithelioid, sarcomatoid, and biphasic mean?
These describe how the cancer cells look under a microscope. Epithelioid cells, the most common type at roughly 6 in 10 cases, tend to have a better outlook. Sarcomatoid cells are less common and tend to be more aggressive. Biphasic mesothelioma is a mix of both epithelioid and sarcomatoid cells.
Does cell type affect treatment?
Yes. Cell type, along with location and stage, helps guide treatment decisions and gives a general sense of what to expect, since epithelioid mesothelioma tends to respond somewhat better to treatment than sarcomatoid or biphasic types.
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Last updated: 2026-08-18Next planned review: 2027-08-03
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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