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244 Christopherson et al.<br />
1.2.3. Diagnosis Using an Extensive Immunophenotype<br />
The DotScan microarray is being used to accumulate an extensive patient<br />
database of immunophenotypes of myeloid leukemias to establish consensus<br />
patterns for the subtypes. It is likely that an extensive immunophenotype will<br />
be sufficient to classify subtypes of AML, and that expression patterns may<br />
also provide prognostic information not available from the limited<br />
immunophenotype currently obtained by flow cytometry. DNA microarrays<br />
determine mRNA levels, whereas an extensive immunophenotype determined<br />
with the DotScan microarray provides a direct extension of our knowledge of<br />
CD antigens and incorporates antibodies currently in diagnostic use. The<br />
DotScan microarray identifies cell-surface proteins that correlate directly with<br />
cellular function, whereas mRNA levels may not correlate directly with the<br />
leukemia. The antigens determined by flow cytometry in a standard<br />
immunophenotype for AML represent a narrow range of “lineage specific”<br />
markers (Table 1). A broader panel of myeloid antigens including adhesion<br />
molecules such as CD11(a-c), CD18, CD49(a-f), CD62L, activation markers<br />
such as CD71, and a broader panel of myeloid antigens are generally not studied<br />
by flow cytometry.<br />
The WHO classification includes five sub-types of AML with cytogenetic<br />
abnormalities: AML/ETO, inv16, CBF⇓/MYH11, PML-RARα, and MLL; this<br />
group will clearly expand with further investigation. These cytogenetic abnormalities<br />
may correlate with changes in expression of surface molecules<br />
observed as part of an extensive immunophenotype. For example, Munoz et al.<br />
(11) found differences between AML groups with and without internal tandem<br />
duplications (ITD) of the FLT3 gene. A diagnosis of FAB subtype AML-M5<br />
and expression of monocytic markers CD36 and CD11b were more frequent in<br />
FLT3/ITD(+) patients, whereas stem cell markers CD34 and CD117 were less<br />
common. <strong>Myeloid</strong> leukemias characterized by specific immunophenotypes are<br />
uncommon, but CD13, CD33, and CD117 are expressed in AML-M0 (12,13),<br />
glycophorin A (CD235a) in AML-M6, and CD41 and CD61 in AML-M7. Furthermore,<br />
the extensive immunophenotype available from the DotScan<br />
microarray should result in additional patterns of antigen expression within<br />
these subtypes that increase the confidence of classification (14). Other subgroups<br />
of AML are likely to have characteristic consensus immunophenotypes.<br />
For example, Paietta (15) found diagnostic power for acute promyelocytic leukemia<br />
(APML) with three antigens—HLA-DR, CD11a, and CD18. Characteristic<br />
dot patterns or surface molecule profiles from the DotScan microarray for<br />
AMLs may allow classification and diagnosis of a wider range of subtypes.<br />
These immunological classifications may not necessarily correspond with previous<br />
morphological criteria, and a new classification system may evolve using<br />
surface molecule profiles from the DotScan microarray.