Mesothelial tumors
Mesothelioma - epithelioid

Topic Completed: 1 November 2013

Revised: 2 October 2019

Copyright: 2003-2019,, Inc.

PubMed Search: Epithelioid mesothelioma[TIAB] pleural

See Also: Mesothelioma

Vaidehi Avadhani, M.D.
Page views in 2019: 3,459
Page views in 2020 to date: 1,534
Cite this page: Avadhani V. Mesothelioma - epithelioid. website. Accessed February 27th, 2020.
Definition / general
  • Most frequent histologic type of malignant mesothelioma
Case reports
  • 73 year old man with bilateral pleural effusions, lung nodules and pleural thickening (Case of the Week #476)
Microscopic (histologic) description
  • Composed of oval, polygonal or cuboidal cells, with multiple secondary patterns:
    • Tubulopapillary:
      • Characteristic papillary growth pattern
      • Tumor cells with round nuclei, moderate amounts of eosinophilic cytoplasm and conspicuous nucleoli
      • Elongated tubular structures may also be seen
      • Must distinguish from micropapillary pattern, which has a poorer prognosis
  • Other patterns:
    • Acinar: elongated or branching gland-like lumina lined by relatively bland cuboidal cells
    • Adenomatoid
    • Adenoid cystic: cribriform and tubular patterns separated by fibrous stroma
    • Clear cell: mesothelial cells with clear cytoplasm
    • Deciduoid: sheets of large polygonal cells with abundant glassy cytoplasm, round vesicular nuclei and prominent nucleoli
    • Micropapillary: has higher incidence of lymphatic invasion
    • Pleomorphic: marked nuclear pleomorphism; if this component is > 10%, has an adverse prognosis
    • Rhabdoid: dyscohesive cells with abundant eosinophilic cytoplasm, eccentric nuclei, prominent nucleoli; variable eosinophilic cytoplasmic inclusion
    • Signet ring cell: clusters or sheets of cells with cytoplasmic vacuoles
    • Small cell: very rare; uniform small round cells with high N:C ratio
    • Solid
    • Trabecular
Microscopic (histologic) images

Contributed by Dr. Ayesha Azam for Case of the Week #476





Cytology description
  • Papillary epithelial type:
    • Papillary fragments and cohesive cell clusters
    • Moderate amount of cytoplasm
    • Round to ovoid nuclei, prominent nuclei
    • Psammoma bodies may be seen (Cancer Cytopathol 2013;121:703)
  • Cohesive epithelioid type:
    • Cohesive groups of cells
    • Nuclei round or oval with some pleomorphism
    • Eccentrically located nuclei occasionally with coarse chromatin
    • Multinucleation is common
    • Variable mitotic figures
    • Asbestos bodies maybe seen
Positive stains
  • Calretinin: both nuclear and cytoplasmic staining; useful to distinguish mesothelioma and lung adenocarcinoma
  • Keratin 5 / 6: expressed in epithelioid mesothelioma but negative in sarcomatoid mesothelioma
  • Podoplanin (D2-40): membranous and apical staining; may be expressed in squamous cell carcinoma of lung and serous carcinoma, synovial sarcoma and angiosarcoma
  • WT1: useful to distinguish mesothelioma from renal cell carcinoma and squamous cell carcinoma (Hum Pathol 2013;44:1)
Negative stains
Electron microscopy description
  • Very long, thin apical microvilli that do not have a glycocalyx
  • Adenocarcinomas have shorter microvilli, have a glycocalyx and perinuclear tonofilament bundles
Differential diagnosis
Board review style question #1
Which set of antibodies is useful for distinguishing pleural malignant mesothelioma from lung adenocarcinoma?

A. WT1, CA125, BerEP4 (EpCAM)
B. CA125, BerEP4, Calretinin
C. BerEP4, Calretinin, AE1/AE3
D. WT1, BerEP4, Calretinin
E. WT1, BerEP4, AE1/AE3
Board review answer #1
D. WT1 and calretinin are specific for mesothelial cells and BerEP4 is specific for lung adenocarcinoma. CA125 and AE1/AE3 are immunoreactive in both mesothelioma and adenocarcinoma.
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