AML (M7)

Acute Megakaryoblastic Leukemia

• Relatively uncommon form of leukemia characterized by extensive proliferation of magakaryoblasts and atypical megakaryocytes.
  
  
• Increased recognition of this entity has been largely aided by the use of platelet peroxidase (PPO) ultrastructural studies. Platelet peroxidase is distinct from Myeloperoxidase; it is specific for the megakaryocytic cell line. This enzyme appears early in the differentiation of these cells and is localized in the nuclear membrane and endoplasmic reticulum.
  
  
• Originally, M7 was not part of FAB classification because it could not be identified by conventional morphologic and cytochemical studies.
  
  
• The blasts display a wide range of morphology from small cells with scant cytoplasm and dense chromatin to large cells with a moderate amount of cytoplasm and a fine reticulated chromatin pattern.
  
  
• Cytoplasmic projections are sometimes present.
  
  
• Azurophilic granules resembling early granular megakaryocytes can be seen in some cases.
  
  
• Presence of megakaryocytic fragments in the PB is suggestive of M7.
  
  
• Conventional cytochemistry studies can help support the diagnosis, but are not diagnostic.
  
  
• The Myeloperoxidase and Sudan Black B reactions are negative.
  
  
• Reactions to acid phosphatase (PAS) and alpha-napthyl acetate esterase (ANAE) are usually positive.
  
  
• The combination of a positive ANAE and a negative alphanaphthyl butyrate esterase rules out monocytic leukemia and is highly suggestive of megakaryoblastic lineage.
  
  
• Can use immunocytochemical method to demonstrate platelet specific antigens.
  
  
• Antibodies against factor 8 related antigen and against the surface Glycoprotein 2b/2c (fibrinogen receptor, CD 41) are the most sensitive and specific immunologic markers of M7.
  
  
• Electron microscopy studies for platelet peroxidase are recommended when possible.
  
  
• Distinguished by the utltrastructural demonstration of platelet peroxidase or use of antibodies directed against platelet antigens.

PROGNOSIS

Very poor (days to a few months)