The document defines asynchronous antigen expression as antigens expressed during normal maturation that are found simultaneously on malignant cells, which can lead to misinterpretation and incorrect treatment if not properly understood. Aberrant antigen expression is defined as antigens unexpected for the lineage in question but that do not change the lineage assignment. The diagnosis of acute leukemia of ambiguous lineage is based on flow cytometric immunophenotyping showing no clear evidence of differentiation along a single lineage.

3. Asynchronous antigen expression is defined as:
‘The situation where antigens that are expressed during normal maturation
are found simultaneously on the malignant cells.’
‘These patterns are of critical importance; misinterpretation may result in
inappropriate lineage assignation and incorrect treatment.
Aberrant antigen expression is defined as:
‘Expression of an antigen that is unexpected on the lineage in question (i.e. is not
present during normal maturation), but which does not alter the lineage assignation.’

4. Expression an antigen of
a different lineage
Expression an antigen of
a different maturational stage
Mature B-ALL with asynchronous expression of CD34 Common B-ALL with aberrant expression of CD33/CD13

5. Expression an antigen of
a different lineage
Expression an antigen of
a different maturational stage
Mature B-ALL with asynchronous expression of CD34
AML M3 v
AML
AML M2
AML M4 Eo
AML
ALL Pro-B

6. The diagnosis of acute leukemia of ambiguous lineage is based on
flow cytometric immunophenotyping.
No clear evidence of differentiation along a single lineage
Acute leukemia of
Ambiguous Lineage
AUL
Undifferentiated AL
MPALs
Mixed phenotype
Acute Leukemias
Mixed
lineage
Mixed
phenotype
[ Bi-lineage ]
More than One Blast Populations
Single Blast Population
[ Bi-phenotypic ]

7. CD19
The diagnosis of acute leukemia of ambiguous lineage is based on
flow cytometric immunophenotyping.
No clear evidence of differentiation along a single lineage
Acute leukemia of
Ambiguous Lineage
AUL
Undifferentiated AL
MPALs
Mixed phenotype
Acute Leukemias
Mixed
lineage
Mixed
phenotype
[ Bi-lineage ]
[ Bi-phenotypic ]
MB
CD19
MPO
MPO

10. Myeloid

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