Malignant mesothelioma

Malignant mesothelioma, also mesothelioma, is a form of cancer. It arises from the mesothelium.

Malignant mesothelioma
Diagnosis in short
Malignant mesothelioma. H&E stain.
LM	infiltrative atypical cells (epithelioid, spindled or both)
Subtypes	biphasic mesothelioma, epithelioid mesothelioma, desmoplastic mesothelioma, sarcomatoid mesothelioma.
LM DDx	mesothelial hyperplasia, fibrosing pleuritis, adenocarcinoma - esp. lung, serous carcinoma
IHC	calretinin +ve, D2-40 +ve, CK5/6 +ve, WT-1 +ve, CK7 +ve, CEA -ve, TTF-1 -ve
Molecular	p16 deletion
Site	lung, peritoneum, omentum, pericardium
Clinical history	asbestos exposure
Prevalence	rare
Prognosis	very poor

It should not be confused with benign multicystic mesothelioma and benign papillary mesothelioma.

General

• Poor prognosis - median survival <12 months.

Locations:

• Lung.
• Primary peritoneal.
• Primary pericardial.

Epidemiology:

• Strong association with asbestos exposure.

Note:

• No association with smoking.^{[citation needed]}

Asbestos

Conditions associated with asbestos exposure (mnemonic PALM):

• Pleural plaques.
• Asbestosis.
• Lung carcinoma.
• Malignant mesothelioma.

Possible association with asbestos exposure:

• Gestational trophoblastic disease.

Microscopic

Features:

• Infiltrative atypical cells - key feature.
  • Infiltration into fat - diagnostic.
  • +/-Epithelioid cells - may be cytologically bland, i.e. benign appearing.
    • Variable architecture: sheets, microglandular, tubulopapillary.
    • +/-Psammoma bodies.
  • +/-Spindle cells.
• +/-Ferruginous body - strongly supportive.
  • Looks like a (twirling) baton - segemented appearance, brown colour.
  • Thin (asbestos) fiber in the core.

Notes:

• Asbestos body is not strictly speaking a synonym for ferruginous body.
• Don't diagnose mesothelioma in situ.^{[citation needed]}

DDx:

• Fibrosing pleuritis - should not have nodules, more cellular on the aspect adjacent to the effusion.
• Reactive mesothelial cells - may be atypical.
• Mesothelial hyperplasia.
• Adenocarcinoma - esp. lung adenocarcinoma.
• Serous carcinoma.

Images

• 

  Ferruginous body. (WC)

• 

  MM - low mag.

• 

  MM - intermed. mag.

• 

  MM - high mag.

• 

  MM - very high mag.

• 

  MM - calretinin - intermed. mag.

• 

  MM - calretinin - high mag.

Subtypes

List of subtypes - mnemonic BEDS:

• Biphasic mesothelioma.
  • 10%+ of epithelioid & 10%+ sarcomatoid.
• Epithelioid mesothelioma.
• Desmoplastic mesothelioma.
  • Should be 50%+ dense tissue with storiform pattern & atypical cells.
• Sarcomatoid mesothelioma.

Other:

• Small cell mesothelioma.

Stains

• PASD -ve.
• Mucicarmine -ve.
  • Typically +ve in adenocarcinoma.

IHC

Mesothelioma versus mesothelial hyperplasia

Features:

• EMA +ve ~100% (vs. ~10%).
• Desmin -ve ~5% (vs. ~85%).
• GLUT1 +ve ~50% (vs. ~10%)
• p53 +ve ~50% (vs. ~2%).

Note:

• The above are not very useful in individual cases.
• A simple pankeratin is useful for seening where epithelial cells are.

Mesothelioma versus adenocarcinoma

• Several panel exists - no agreed upon best panel.
  • Usually two carcinoma markers + two mesothelial markers.

Panel:

• Mesothelial markers:
  • Calretinin.
  • WT-1.
  • D2-40.
  • CK5/6.
• Carcinoma markers:
  • CEA (monoclonal and polyclonal).
  • TTF-1.
  • Ber-EP4.
  • MOC-31.
  • CD15.

Other carcinoma markers:

• PAX-8.
• Claudin-4.
  • Mesothelioma may be focally positive.

Molecular

• p16 deletion by FISH.

Notes:

• p16 IHC does not give the same result.
• Sensitivity of p16 deletion is low.

See also

• Lung tumours.
• Omentum.
• Empyema peel.