MPAL

Final lineage in MPAL requires integration of additional molecular features, so assigments made by flow should be regarded as "provisional" pending full molecular assessment.‎

‎.

Requirements to assign myeloid lineage in MPAL The assignment of myeloid lineage recognises MPO expression to be a defining marker of myeloid lineage. However MPO is expressed only by around 80% of AML cases. The assignment of myeloid lineage can therefore also be made if monocytic lineage can be established, requiring at least of 5 possible lineage markers to be detected (although only 3 of these can be established by flow cytometry).
Marker option 1
Myeloperoxidase (MPO)	This marker alone is sufficient to establish myeloid lineage provided it meets the intensity definition - intensity should be at least half of that of mature neutrophils in at least of proportion of cells.
marker option 2
If MPO does not meet criteria for myeloid lineage, then myeloid lineage may still be assigned through demonstration of monocytic lineage. This can be assigned by the detection of at least two of the following features: By flow cytometry: CD11c, CD14, CD64; by other approaches: raised lysozyme in serum or urine or non-specific esterase in malignant cells (enzyme cytochemistry)

‎‎.

Lineage assignments 2 - defining B-lymphoid lineage in MPAL For B-lymphoid lineage assignment the key lineage-marker is CD19. However, this marker has recognised aberrant expression in AML cases so additional criteria of expression intensity it is required that other markers must be expressed in addition to allow B-lineage assignment.
Marker option 1
Required Strong expression of CD19	To meet the definition of "strong" the expression intensity must exceed that of 50% of normal B lymphocytes
In addition: CD10, CD22, or CD79a	If CD19 is strong then B-lineage can be assigned if there is at least ONE of these additional markers
Marker option 2
Required Weak expression of CD19	To meet the definition of "weak" the expression intensity must be less than that of 50% of normal B lymphocytes
In addition: CD10, CD22, or CD79a	If CD19 is strong then B-lineage can be assigned if there is at least TWO of these additional markers

‎.

Lineage assignments 3 - defining T-lymphoid lineage in MPAL For T-lymphoid lineage assignment the key lineage-marker is CD3. Provided that this marker meets the intensity criteria then it is T-lineage defining in MPAL. This expression can be determined either by CD3 detection by flow cytometry OR by immunocytochemistry on trephine.
Marker requirement
Either CD3 surface or cytoplasm (strong)	To meet the definition of "strong" the expression intensity must exceed that of 50% of normal T lymphocytes
Or CD3 by immunocytochemistry (strong)	For immunohistochemistry it is important a non-zeta chain reagent is used

‎.

Lineage assignments 4 - defining undifferentiated leukaemia This is a difficult area where the diagnosis of acute leukaemia is suspected but no criteria for lineage assignment can be made i.e. the cases do not meet any of the criteria for myeloid, B-lymphoid, or T-lymphoid lineage given above. An important aspect of this group is to exclude the possibility of rare entities that can mimic AML: these include non-haemaotopoietic neoplasm and blastic plasma cell dendritic neoplasm.
Marker requirement 1
Required No lineage assignment can be made for myeloid, B-lymphoid or T-lymphoid using the criteria above
Marker requirement 2
No more than one lineage-associated (but not lineage-defining marker) for any lineage should be expressed
Marker requirement 3
Markers mainly associated with the primitive nature of leukaemic cells do not allow lineage assignment (e.g. CD34, TdT, CD7, CD56, CS38) and are frequently seen in undifferentiated acute leukaemia