Flow cytometry of the marrow aspirate sample is the technique used to phenotype the leukemic cells to allow better classification as to the type of acute leukemia. Allows differentiation into categories of:
- Precursor B-ALL
- Mature B-ALL (Burkitt’s lymphoma)
- T-ALL
- AML (acute myelogenous leukemia)
- Biphenotypic leukemia (blast cells show markers of more than one lineage)
- Bilineage leukemia (two populations of blast cells exist, both with different phenotypes)
Many blasts have aberrant expression of different lineage markers (example, many pre-B ALL cases also co-express a myeloid marker) but there are specific diagnostic criteria to call a leukemia truly biphenotypic (rare).
Expression of markers parallels the cellular development through hematopoiesis from stem cell, to progenitor cells, to immature blood cells, to fully mature blood cell.
Many of these phenotypic markers are cell surface clusters of differentiation, although some are intracellular (cytoplasmic) markers. Most are only expressed on highly immature cells.
Marker |
Comments |
Cytoplasmic TdT (Terminal Deoxynucleotide Transferase) |
Found in most ALL cases but also a proportion of AML. |
CD34 |
Common stem cell marker. Marker of cellular immaturity. |
HLA-DR |
Precursor B-cell, AML (negative in M3 Acute Promyelocytic Leukemia) |
CD 79a |
Precursor B-cell. Importantly, specific for B-lineage ALL. |
CD22 |
Precursor B-cell |
CD10 |
Precursor B-cell (called the common ALL antigen) |
CD19 |
Precursor B-cell |
CD20 |
Mature B-cell (seen in Burkitt’s and Burkitt’s like leukemia/lymphomas). Target for Rituximab in more mature B-cell lymphomas. Negative on true precursor B-ALL cases. |
CD3 (cytoplasmic or cell surface) |
T-ALL |
CD4 |
T-ALL (often negative, depending on where in stage of T-cell ontogeny malignant clone developed). |
CD8 |
T-ALL (often negative, depending on where in stage of T-cell ontogeny malignant clone developed). |
CD7 |
T-ALL |
CD1a |
T-ALL |
CD2 |
T-ALL |
CD13 |
AML |
CD14 |
AML |
CD15 |
AML |
CD33 |
AML |
CD41/61 – Markers of Megakaryocytic Development |
AML, Helps to differentiate M7 (Megakaryocytic Variant) |
CD117 |
Myeloid / Stem Cell |
Glycophorin A – Markers of Erythrocytic Development |
AML, Helps to differentiate M6 (Erythroblastic Variant) |
