Peritoneum, omentum and mesentery
Mesothelial lesions
Epithelioid mesothelioma

Author: Aysha Mubeen, M.D. (see Authors page)
Editor: Raul S. Gonzalez, M.D.
Deputy Editor Review: Debra Zynger, M.D.

Revised: 25 July 2018, last major update February 2018

Copyright: (c) 2003-2018,, Inc.

PubMed Search: Peritoneum epithelioid mesothelioma
Cite this page: Mubeen, A. Epithelioid mesothelioma. website. Accessed November 12th, 2018.
Definition / general
  • Mesothelioma is a neoplasm arising from mesothelial cells that line serous cavities, such as the pleura and peritoneum
  • Pleural mesothelioma is much more common than peritoneal mesothelioma
  • Epithelioid mesothelioma is the most frequent histologic type of malignant mesothelioma; sarcomatoid and biphasic subtypes are less common
  • 20 - 33% of malignant mesothelioma arises in the peritoneum (Semin Oncol 2002;29:51)
Essential features
  • Hallmark of epithelioid mesothelioma is the epithelioid cells which are polygonal cells with moderate to abundant eosinophilic cytoplasm, vesicular round nuclei and prominent nucleolus; often mimic nonneoplastic, reactive mesothelial cells (Arch Pathol Lab Med 2018;142:89)
  • The most common histologic patterns of epithelioid mesothelioma are tubulopapillary, adenomatoid, solid well differentiated, solid poorly differentiated and acinar (Arch Pathol Lab Med 2012;136:241)
  • Myxoid variant of peritoneal epithelioid mesothelioma is extremely rare with only 5 reported cases
  • Often due to asbestos exposure, whether in the pleura, peritoneum and pericardium; cumulative asbestos exposure is directly proportional to risk of cancer (J Med Case Rep 2008;2:121)
  • Asbestos fibers lead to chronic inflammation, which causes the release of free radicals
  • Latent period between asbestos exposure and disease averages 20 - 30 years (Cancer Treat Rev 2012;38:605)
Clinical features
  • No distinctive symptoms, causing difficulties in diagnosis and treatment
  • When symptomatic, usually present with abdominal pain, ascites and abdominal distention
Radiology images

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CT with dilated loops of bowel

Prognostic factors
Case reports
  • Systemic chemotherapy
  • Cytoreductive and palliative surgery
Clinical images

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Fig D: bilateral
intratubal masses

Gross description
  • Diffuse thickening or multiple nodules on the peritoneum
  • Myxoid variant is gelatinous
Microscopic (histologic) description
  • Epithelioid cells are arranged in different patterns (which form the basis of the different subtypes of epithelioid mesothelioma)
  • Form tubules and papillae with / without psammoma bodies (tubulopapillary variant), gland-like structures (acinar variant) and are in solid sheets, nests or cords (solid variant)
  • Myxoid variant:
    • Dyscohesive medium to large epithelioid cells with a moderate to abundant amount of eosinophilic cytoplasm dispersed in a myxoid background
    • Some cells can have intracytoplasmic clear vacuoles
    • Nuclei with coarse chromatin and prominent nucleoli
    • Mitotic figures are usually inconspicuous
    • Difficulty to differentiate from other myxoid lesions of the peritoneum (e.g. adenocarcinoma) thus panel of immunohistochemical markers is generally required
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by Aysha Mubeen, M.D.

Epithelioid mesothelioma (pleural)

Myxoid variant of peritoneal mesothelioma



Virtual slides

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Epithelioid mesothelioma: 70 year old man with pleural effusion

Cytology description
  • Clusters of epithelioid cells (morulae) with knobby contour
  • Abundant cytoplasm, round nuclei and prominent nucleoli
  • Mild atypia
Cytology images

Images hosted on PathOut server:

Contributed by Aysha Mubeen, M.D.

Cell block, myxoid variant

ThinPrep, myxoid variant

DiffQuik, myxoid variant

Positive stains
Negative stains
Electron microscopy description
  • Very long, thin apical microvilli and the absence of glycocalyx (compared to adenocarcinoma, which has shorter villi)
Electron microscopy images

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Various images

Additional references
Board review question #1
Which of the following stains is positive in the myxoid variant of epithelioid mesothelioma and helps to differentiate it from mucinous adenocarcinoma?

  1. B72.3
  2. Claudin4
  3. D2-40
  4. MOC31
Board review answer #1
C. D2-40