Acute leukaemia types

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Sections

• Establishing the primitive nature of AML blast cells (CD45 gating and primitive markers) click to visit section
• The AML phenotype (expected markers expressed by most AML cases or those with specific differetiation) click to visit section
• Abberent markers in AML (Abberrent makers that are frequently encountered) click to visit section
• Important additional notes 1: recognising difficult subtypes 2: clues suggesting MPAL or ETP-ALL) click to visit section

(note: for further information on any marker or section click the blue highlighted text)

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MARKERS USEFUL TO CONFIRM PRIMITIVE NATURE OF BLAST CELLS
Useful markers of primitive nature The first step in AML diagnosis to establish the primitive nature of the abnormal cells: (1) Typically AML blasts have low CD45 expression and cause low side scatter. This means that they form a relatively uniform and distinctive population that is clearly separate from that of lymphocytes on CD45/SSc plots (for further details see this section) also not all AML forms may fit this pattern - particularly APL and monocytic AML. (2) Additional markers often expressed on myeloid cells may help confirm the primitive nature of the cells: in AML this is most often CD34, although other markers may contribute.
CD45	A marker expressed by all leukocytes and their precursors. In AML expression is characteristically "weak" i.e. significantly less intense than normal lymphocytes or monocytes. In monocytic AML expression may be stronger.
CD34	Frequently expressed by AML blast cells (40-80% of cases) - most often in less differentiated forms of AML. Expression is also seein frequently (and often more strongly) in ALL

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MARKERS USEFUL TO CONFIRM MYELOID LINEAGE OR DIFFERENTIATION
Frequently expressed "general" markers of myeloid lineage Some additional markers are regarded as indicating primitive nature when expressed by AML blasts; these markers may be more usually assocated with T-lineage or B-lineage ALL, but when expressed in AML they are considered to indicate less differentiated forms.
MPO	A strong lineage marker for AML (expressed in around 80% of cases) but generally in those with granulocytic maturation. When detected by flow cytometry is diagnostic of myeloid differentiation (either AML or MPAL)
CD117	An early marker of myeloid lineage, seen in up to 80% of AML and vauable in recognising more primitive differentaiion forms (note that aberrant expression is seen in up to 20% of ALL cases)
CD33	A good marker for AML, particularly for those cases with granulocytic maturation, CD33 is often less strongly expressed in AML with monocytic dfferentiation and strongly expressed in APL.
CD13	A good lineage marker for AML that is acquired a little later in differentation than CD117 or CD33; expression of CD13 is often higher than CD33 in AML with monocytic differentiation.
Confirmatory markers of AML or markers of subtype Some additional markers are regarded as indicating primitive nature when expressed by AML blasts; these markers may be more usually assocated with T-lineage or B-lineage ALL, but when expressed in AML they are considered to indicate less differentiated forms.
Granulocytic lineage markers
CD10	One of tne of the first lineage-markers acquired in AML with good relative specificity
CD11b	One of tne of the first lineage-markers acquired in AML with good relative specificity
Monocytic lineage markers
CD11c	One of tne of the first lineage-markers acquired in AML with good relative specificity
CD14	A good marker for AML that is often less strongly expressed in monocytic forms
CD64	A good lineage marker for AML aquired a little later, higher than CD13 in monocytic forms
Erythroid lineage markers
CD14	A good marker for AML that is often less strongly expressed in monocytic forms
CD64	A good lineage marker for AML aquired a little later, higher than CD13 in monocytic forms
Megakaryocytic lineage markers
CD14	A good marker for AML that is often less strongly expressed in monocytic forms
CD64	A good lineage marker for AML aquired a little later, higher than CD13 in monocytic forms

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NON MYELOID MARKERS FREQUENTLY "ABERENTLY" EXPRESSED IN AML
Markers of lymphoid lineage indicating primitive dfferentiation in AML Some additional markers are regarded as indicating primitive nature when expressed by AML blasts; these markers may be more usually assocated with T-lineage or B-lineage ALL, but when expressed in AML they are considered to indicate less differentiated forms.
TDT	Expressed in some cases of AML (5-20%) particularly in less differentiated blast cells, often on a sub-population of cells. More typically associated with primitive ALL blast cells.
CD7	Predominantly seen as a T-cell antigen, CD7 tends may be expressed by AML blasts (20-40%) where it most often indicates a more primitive forms or MPAL. CD7 is most consistently a marker of T-lineage (including T-ALL and more mature froms).
Markers of lymphoid differentation abererantly expressed in AML Some additional markers are regarded as indicating primitive nature when expressed by AML blasts; these markers may be more usually assocated with T-lineage or B-lineage ALL, but when expressed in AML they are considered to indicate less differentiated forms.
TDT	Expressed in some cases of AML (5-20%) particularly in less differentiated blast cells, often on a sub-population of cells. More typically associated with primitive ALL blast cells.
CD7	Predominantly seen as a T-cell antigen, CD7 tends may be expressed by AML blasts (20-40%) where it most often indicates a more primitive forms or MPAL. CD7 is most consistently a marker of T-lineage (including T-ALL and more mature froms).

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IMPORTANT ADDITIONAL POINTS
AML subtypes with distinctive phenotype The first step in AML diagnosis to establish the primitive nature of the abnormal cells: (1) Typically AML blasts have low CD45 expression and cause low side scatter. This means that they form a relatively uniform and distinctive population that is clearly separate from that of lymphocytes on CD45/SSc plots (for further details see this section) also not all AML forms may fit this pattern - particularly APL and monocytic AML. (2) Additional markers often expressed on myeloid cells may help confirm the primitive nature of the cells: in AML this is most often CD34, although other markers may contribute.
Mixed Phenotype Acute leukaemia (MPAL)
Formerly known as leukaemia of ambiguous lineage
Early T-precursor acute lymphoblastic leukaemia (ETP-ALL)
A (relatively new entity)
Acute leukaemia types with features of mixed phenotype The first step in AML diagnosis to establish the primitive nature of the abnormal cells: (1) Typically AML blasts have low CD45 expression and cause low side scatter. This means that they form a relatively uniform and distinctive population that is clearly separate from that of lymphocytes on CD45/SSc plots (for further details see this section) also not all AML forms may fit this pattern - particularly APL and monocytic AML. (2) Additional markers often expressed on myeloid cells may help confirm the primitive nature of the cells: in AML this is most often CD34, although other markers may contribute.
Mixed Phenotype Acute leukaemia (MPAL)
Formerly known as leukaemia of ambiguous lineage
Early T-precursor acute lymphoblastic leukaemia (ETP-ALL)
A (relatively new entity)
Non-haematopoietic tumours
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