Assignment of lineage is very important in the
diagnosis of acute leukemia, as treatments for acute myeloid
leukemia (AML) and acute lymphoblastic leukemia
(ALL) are diff erent. Identifi cation of myeloid and lymphoid
lineage may be recognized based on cellular morphology,
cytochemical staining, and immunophenotyping (expression
of lineage-specifi c antigens). The diagnosis and
classifi cation of hematopoietic neoplasms have greatly
improved from the general application of immunophenotyping
during the past two decades. The identifi cation of
hematopoietic neoplasms by their association to normal
hematopoietic lineages and stages of diff erentiation is a
basic datum of current classifi cation systems, such as
the World Health Organization (WHO) classifi cation. This
information is largely provided by immunophenotyping
and has resulted in the addition of immunophenotypic
data into the defi nition of many hematopoietic neoplasms.
At present, the certain diagnosis and classifi cation of
hematopoietic neoplasms cannot be confi dently made
without immunophenotypic data.1,2,3 Myeloid antigen
expression in acute leukemia that is morphologically