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Epithelioid Mesothelioma

From WikiMesothelioma — Mesothelioma Knowledge Base


Epithelioid Mesothelioma
Also Known As Epithelial mesothelioma
Share of Cases ~60–70% (most common)
Prognosis Rank Best of the 3 subtypes
Median Survival ~16 months (multi-institutional series)
Cell Shape Cuboidal, uniform, epithelial-like
Key Markers Calretinin+, WT1+, D2-40+
Peak Latency 20–50 years

Executive Summary

Epithelioid mesothelioma is the most common of the three histological subtypes of malignant mesothelioma, accounting for approximately 60–70% of pleural cases and an even higher share — roughly 79–91% — of peritoneal cases in surgical series.[1][2] It is defined by uniform, cuboidal, epithelial-like tumor cells, and among the subtypes it carries the best prognosis and the strongest response to treatment.[3]

Survival is meaningfully better than for sarcomatoid or biphasic disease, but it is not uniform within the subtype. A 776-patient multi-institutional study found a median overall survival of about 16 months for epithelioid pleural mesothelioma, and showed that nuclear grade stratifies patients into distinct groups — from 29 months for low-grade tumors without necrosis down to 8 months for the highest-grade tumors.[4][5] This is why the 2021 WHO Classification of Thoracic Tumours recommends nuclear grading for all epithelioid mesotheliomas.[4]

Because epithelioid histology predicts a better response to surgery, chemotherapy, and immunotherapy, an epithelioid diagnosis often expands a patient's treatment options.[2][6] Patients with epithelioid mesothelioma retain the same rights to asbestos trust fund and lawsuit compensation as those with any other subtype.[7]

At-a-Glance

Epithelioid mesothelioma at a glance:

  • Most common subtype — about 60–70% of pleural cases — and roughly 79–91% of peritoneal cases in surgical series, making it the subtype most patients are diagnosed with[1][2]
  • Best prognosis of the three subtypes — epithelioid consistently outlives sarcomatoid and biphasic disease when matched for stage and treatment[3]
  • Median survival around 16 months in a 776-patient study — but nuclear grade splits that into groups ranging from 29 months to 8 months[4]
  • Nuclear grading now standard — the 2021 WHO classification recommends grading every epithelioid mesothelioma by nuclear atypia and mitotic count[4]
  • Identified by immunohistochemistry — epithelioid tumors are typically calretinin-positive, WT1-positive, and D2-40-positive, which distinguishes mesothelioma from lung and other cancers[8]
  • Responds best to aggressive treatment — epithelioid histology is an independent predictor of improved survival after cytoreductive surgery with HIPEC for peritoneal disease[2]
  • Eligible for first-line immunotherapy — nivolumab plus ipilimumab is FDA-approved first-line for unresectable pleural mesothelioma, including epithelioid disease[6]
  • Multiple growth patterns — tubulopapillary, acinar, solid, trabecular, micropapillary, and pleomorphic patterns exist, and they carry different outlooks[4]
  • Caused by asbestos — like all mesothelioma, epithelioid disease follows asbestos exposure by 20 to 50 years[9]
  • Full compensation rights — trust funds, lawsuits, and VA benefits are available regardless of cell type[7]

Key Facts

Measure Finding (Source)
Share of pleural cases ~60–70% — most common subtype[1]
Share of peritoneal cases (surgical) ~79–91% — Yan et al., multi-institutional series[2]
Prognosis among subtypes Best of epithelioid, sarcomatoid, biphasic[3]
Median overall survival ~16 months — Rosen et al., 776 cases, 2018[4]
Nuclear grade I, no necrosis 29 months median survival[4]
Nuclear grade III 8 months median survival[4]
Immunohistochemistry markers Calretinin+, WT1+, D2-40+[8]
First-line systemic therapy Nivolumab + ipilimumab or platinum/pemetrexed[6]
Peritoneal treatment CRS + HIPEC — epithelioid predicts better survival[2]
Typical latency 20–50 years after asbestos exposure[9]

What Is Epithelioid Mesothelioma?

Epithelioid mesothelioma is the most common form of malignant mesothelioma, defined by the appearance of its tumor cells under the microscope. The cells are cuboidal, uniform, and epithelial-like — resembling the normal cells that line body cavities — and they tend to grow in more organized patterns than the other subtypes.[3] This orderly cell structure is part of why epithelioid disease behaves less aggressively.

Mesothelioma is divided into three histological subtypes based on cell shape: epithelioid, sarcomatoid, and biphasic (a mix of both). Epithelioid accounts for roughly 60–70% of pleural cases, sarcomatoid for the smallest share, and biphasic for the remainder.[1] In peritoneal mesothelioma, the epithelioid subtype is even more dominant, making up 79–91% of cases in surgical series.[2]

The subtype matters because it is one of the two strongest predictors of prognosis, alongside stage. An epithelioid diagnosis is, relatively speaking, the most favorable of the three — a distinction that directly affects which treatments a patient can pursue.[3] Understanding the difference between the subtypes is central to understanding a mesothelioma diagnosis; see also Sarcomatoid Mesothelioma and Biphasic Mesothelioma.

How Is Epithelioid Mesothelioma Diagnosed?

Diagnosis requires a tissue biopsy and expert pathology, because epithelioid mesothelioma can resemble other cancers — particularly lung adenocarcinoma and, in the abdomen, ovarian or peritoneal carcinomas. Pathologists rely on immunohistochemistry, staining the tissue for proteins that mark mesothelial origin. Epithelioid mesothelioma is typically positive for calretinin, WT1, and D2-40, while staining negative for markers of the cancers it mimics.[8] On gross examination, pleural mesothelioma appears as a thick, encircling tumor mass arising from the pleura — a bulky rind that can fill much of the chest cavity — as seen in pathology teaching atlases.[10]

Because the distinction between subtypes and their look-alikes changes treatment, specialist pathology review is especially valuable. Mesothelioma is rare, and a general pathologist may not encounter it often; a review at a high-volume center can confirm both the diagnosis and the exact subtype.[11]

The pathology report does more than guide treatment. It becomes the central piece of evidence in an asbestos claim, documenting both the disease and its cell type. An accurate, specialist-confirmed diagnosis strengthens both the medical plan and any legal case.[12]

Why Does Nuclear Grade Matter in Epithelioid Mesothelioma?

Not all epithelioid mesotheliomas behave the same way, and the tool that separates them is nuclear grading. Introduced into routine practice by the 2021 WHO Classification of Thoracic Tumours, nuclear grading scores a tumor on two features: nuclear atypia (how abnormal the cell nuclei look) and mitotic count (how quickly the cells are dividing).[4]

The predictive power of this grading is striking. A 776-patient multi-institutional study of epithelioid pleural mesothelioma found an overall median survival of about 16 months, but when tumors were separated by nuclear grade and the presence of necrosis, four distinct prognostic groups emerged: nuclear grade I tumors without necrosis survived a median of 29 months, an intermediate group 16 months, nuclear grade II tumors with necrosis 10 months, and nuclear grade III tumors 8 months.[4] A validation study in peritoneal epithelioid mesothelioma confirmed that nuclear and combined grade independently predict survival.[13]

For patients, this means two people with the same "epithelioid" diagnosis can face very different outlooks depending on grade — and it underscores why detailed, specialist pathology is worth seeking.[14]

What Are the Growth Patterns of Epithelioid Mesothelioma?

Within the epithelioid subtype, tumors form several architectural patterns, and these carry different prognoses. The recognized patterns include tubulopapillary, acinar (glandular), solid, trabecular, micropapillary, and pleomorphic.[4] The tubulopapillary pattern is generally associated with a more favorable outcome, while solid, micropapillary, and pleomorphic patterns tend to behave more aggressively.

The pleomorphic pattern deserves particular note. Although classified as epithelioid, pleomorphic tumors often behave more like sarcomatoid disease and carry a correspondingly worse prognosis.[4] This is one reason a pathology report may specify the predominant growth pattern in addition to the subtype and grade — the additional detail refines the prognosis and the treatment plan.

How Is Epithelioid Mesothelioma Treated?

Epithelioid histology broadens treatment options because it responds better than the other subtypes to every major therapy. For pleural disease, patients may be candidates for surgery — pleurectomy/decortication or extrapleural pneumonectomy — combined with chemotherapy and, increasingly, immunotherapy.[15] Nivolumab plus ipilimumab is FDA-approved as first-line therapy for unresectable pleural mesothelioma, and platinum/pemetrexed chemotherapy remains a standard backbone.[6]

For peritoneal epithelioid mesothelioma, the transformative treatment is cytoreductive surgery combined with heated intraperitoneal chemotherapy (CRS/HIPEC). In the landmark multi-institutional registry, epithelioid histology was one of four factors independently associated with longer survival after CRS/HIPEC.[2] In practical terms, an epithelioid diagnosis makes a patient a stronger candidate for the aggressive, potentially life-extending surgery available at specialized centers.

The consistent theme is that epithelioid patients should be evaluated at a high-volume mesothelioma center, where the full range of surgical and systemic options — including clinical trials — is on the table.[15]

How Does Epithelioid Compare to Sarcomatoid and Biphasic Mesothelioma?

The three subtypes sit on a spectrum of aggressiveness. Epithelioid is the least aggressive and most treatable. Sarcomatoid — composed of spindle-shaped cells — is the most aggressive, responds poorly to treatment, and carries the shortest survival. Biphasic mesothelioma contains both cell types, and its prognosis depends largely on how much sarcomatoid tissue is present: the more sarcomatoid component, the worse the outlook.[3][14]

This spectrum is why cell type is reported alongside stage as a core determinant of prognosis. It also explains why immunotherapy has been significant across the board — while epithelioid patients have the best absolute survival, checkpoint immunotherapy narrowed the gap for non-epithelioid patients in first-line trials.[6] For a fuller comparison of where these tumors arise, see Pleural vs Peritoneal Mesothelioma and Mesothelioma Prognosis.

Do Epithelioid Mesothelioma Patients Qualify for Compensation?

Yes. Cell type affects prognosis and treatment, but it does not affect legal rights. A diagnosis of epithelioid mesothelioma establishes the same eligibility for asbestos trust fund claims, personal injury lawsuits, and VA benefits as any other subtype.[7][16] Because mesothelioma is almost always caused by asbestos exposure decades earlier, the key task is reconstructing that exposure history to identify responsible manufacturers.[12]

Because every state imposes a statute of limitations — typically one to three years from the date of diagnosis — prompt legal consultation is important regardless of subtype or grade.


⚠ Statute of Limitations Warning: Filing deadlines vary by state from 1-6 years from diagnosis. Texas allows 2 years from diagnosis or discovery. Contact an attorney immediately to preserve your rights.

Frequently Asked Questions

What is epithelioid mesothelioma?

Epithelioid mesothelioma is the most common subtype of malignant mesothelioma, defined by uniform, cuboidal, epithelial-like tumor cells. It accounts for roughly 60–70% of pleural cases and carries the best prognosis of the three subtypes.[1][3]

Is epithelioid mesothelioma the best type to have?

Among mesothelioma subtypes, epithelioid carries the most favorable prognosis and the strongest response to treatment. It is not a good diagnosis in absolute terms, but relative to sarcomatoid and biphasic disease, it offers more treatment options and longer expected survival.[3][4]

What is the survival rate for epithelioid mesothelioma?

A 776-patient study found a median overall survival of about 16 months for epithelioid pleural mesothelioma, ranging from 29 months for low-grade tumors without necrosis to 8 months for the highest-grade tumors. Survival also depends heavily on stage and treatment.[4]

What does nuclear grade mean in epithelioid mesothelioma?

Nuclear grade scores a tumor by nuclear atypia and how fast its cells divide, sorting epithelioid mesothelioma into grades I through III. Higher grade predicts shorter survival, which is why the 2021 WHO classification recommends grading every epithelioid mesothelioma.[4]

How is epithelioid mesothelioma diagnosed?

Diagnosis requires a biopsy and immunohistochemistry. Epithelioid mesothelioma is typically positive for calretinin, WT1, and D2-40, which distinguishes it from lung and other cancers it can resemble. Specialist pathology review is recommended for this rare cancer.[8][11]

Does having epithelioid mesothelioma affect my legal claim?

No. All mesothelioma subtypes qualify for asbestos trust fund claims, lawsuits, and VA benefits. Cell type affects prognosis and treatment, not your legal rights.[7][16]

Quick Statistics

  • ~60–70% of pleural mesothelioma cases are epithelioid — the most common subtype[1]
  • ~79–91% of peritoneal cases (surgical series) are epithelioid[2]
  • 16 months — median overall survival in a 776-patient epithelioid study[4]
  • 29 vs. 8 months — survival gap between the lowest and highest nuclear grades[4]
  • 3 — histological subtypes: epithelioid, sarcomatoid, biphasic[3]
  • Calretinin, WT1, D2-40 — the immunohistochemistry markers that identify epithelioid mesothelioma[8]
  • 6 — recognized epithelioid growth patterns, from tubulopapillary to pleomorphic[4]
  • 20–50 years — latency from asbestos exposure to diagnosis[9]


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References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Types of Mesothelioma, Mesothelioma Lawyer Center.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Yan TD, Deraco M, Baratti D, et al. Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy for malignant peritoneal mesothelioma: multi-institutional experience. J Clin Oncol. 2009;27(36):6237-42. PMID: 19917862. doi:10.1200/JCO.2009.23.9640.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Mesothelioma Cell Types, Mesothelioma.net.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 Rosen LE, Karrison T, Ananthanarayanan V, et al. Nuclear grade and necrosis predict prognosis in malignant epithelioid pleural mesothelioma: a multi-institutional study. Mod Pathol. 2018;31(4):598-606. PMID: 29327706. doi:10.1038/modpathol.2017.170.
  5. ↑ Cell Types of Mesothelioma, Asbestos and Dust Diseases Research Institute (ADDRI).
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Baas P, Scherpereel A, Nowak AK, et al. First-line nivolumab plus ipilimumab in unresectable malignant pleural mesothelioma (CheckMate 743): a multicentre, randomised, open-label, phase 3 trial. Lancet. 2021;397(10272):375-386. PMID: 33485464. doi:10.1016/S0140-6736(20)32714-8.
  7. ↑ 7.0 7.1 7.2 7.3 Mesothelioma Compensation, Danziger & De Llano.
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Mesothelioma Diagnosis, Mesothelioma.net.
  9. ↑ 9.0 9.1 9.2 Asbestos Exposure, Mesothelioma.net.
  10. ↑ Mesothelioma — gross pathology, WebPath: The Internet Pathology Laboratory, University of Utah (Edward C. Klatt, MD).
  11. ↑ 11.0 11.1 Mesothelioma Diagnosis, Mesothelioma Lawyer Center.
  12. ↑ 12.0 12.1 Filing a Mesothelioma Claim, Danziger & De Llano.
  13. ↑ Benzerdjeb N, Dartigues P, Kepenekian V, et al. Combined grade and nuclear grade are prognosis predictors of epithelioid malignant peritoneal mesothelioma: a multi-institutional retrospective study. Virchows Arch. 2021;479(5):927-936. PMID: 34169365. doi:10.1007/s00428-021-03144-z.
  14. ↑ 14.0 14.1 Mesothelioma Prognosis, Mesothelioma Lawyer Center.
  15. ↑ 15.0 15.1 Mesothelioma Treatment, Mesothelioma Lawyer Center.
  16. ↑ 16.0 16.1 Mesothelioma Settlements, Mesothelioma Attorney.
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