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
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.

See also

• Lung tumours.
• Omentum.
• Empyema peel.