CD34+ Myeloblasts in Hematological Malignancies

Diagnostic Considerations

CD34 immunohistochemistry is particularly valuable for identifying blasts in hypocellular or fibrotic myelodysplastic syndromes (MDS) bone marrow specimens, where morphologic assessment alone may be inadequate 1, 2, 3
The European Hematology Association recommends quantifying CD34+ blasts using immunohistochemistry on bone marrow biopsy, particularly when aspirates are hypocellular or fibrotic 2, 3, 6
The International Society for Laboratory Hematology advises correlating CD34 staining with morphology and cytogenetics to distinguish between hypocellular acute myeloid leukemia (AML), hypocellular MDS, and aplastic anemia 2, 3, 7
Aggressive MDS subtypes show abnormal blast aggregates or clusters (ALIP - abnormally localized immature myeloid precursor cells) that are CD34-positive, associated with poor prognosis and increased progression to acute leukemia 1, 4, 5

The American Society of Hematology suggests that blast percentage <1% in aplastic anemia vs. ≥5% in MDS (or 2-4% in peripheral blood with other MDS features for RAEB-1) 2, 3, 7
The presence of easily identifiable megakaryocytes within architecturally disorganized marrow and reticulin fibrosis favor MDS over aplastic anemia 1, 4, 5
Age-corrected bone marrow cellularity is essential—failure to correct for age leads to overdiagnosis of hypocellular conditions 5, 7

CD34 is expressed on progenitor and early precursor marrow cells, making it one of the most useful markers for counting blasts in tissue sections 1, 4
Flow cytometry and immunohistochemistry show good correlation for CD34 quantification in both MDS and AML, though flow cytometry may yield higher percentages in cases with numerous CD34+ cells 1, 4
The College of American Pathologists recommends performing 500-cell differential count to ensure reliable blast percentage determination, as 100-cell counts have wide confidence intervals 4, 5, 6