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epithelioid mesothelioma pathology outlines : Mesothelioma (pleura)-epithelioid

epithelioid mesothelioma pathology outlines : Mesothelioma (pleura)-epithelioid

Pleura & peritoneum

Pleura mesothelial tumors

Mesothelioma (pleura)-epithelioid

Author: Vaidehi Avadhani, M.D.

Topic Completed: 1 November 2013

Minor changes: 11 January 2021

Copyright: 2003-2021, PathologyOutlines.com, Inc.

PubMed Search: Epithelioid mesothelioma[TIAB] pleural

See Also: Mesothelioma

Vaidehi Avadhani, M.D.

Page views in 2020: 9,942

Page views in 2021 to date: 5,184

Table of Contents

Definition / general | Case reports | Microscopic (histologic) description | Microscopic (histologic) images | Cytology description | Positive stains | Negative stains | Electron microscopy description | Differential diagnosis | Board review style question #1 | Board review style answer #1

Cite this page: Avadhani V. Mesothelioma (pleura)-epithelioid. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/pleuramesotheliomaepithelioid.html. Accessed May 22nd, 2021.

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:


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


  • 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
  • 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 

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
TTF1 and Napsin A: positive in lung adenocarcinoma
PAX8: positive in tumors of Müllerian origin
GATA3 / GCDFP-15 / mammaglobin: positive in breast cancers
MOC31, BerEp4, CEA: positive in adenocarcinoma
Claudin4 may distinguish epithelioid mesothelioma (negative) from metastatic carcinoma to serosal membranes (Am J Clin Pathol 2013;139:611)

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
Adenocarcinoma of breast, colon, lung, pancreas, stomach
Papillary serous carcinoma: more relevant in peritoneal malignant mesothelioma
Renal cell carcinoma: PAX2, PAX8 are very helpful

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 style 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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