Clinical and biological significance of CD34 expression in acute leukemia

From the beginning of its production, monoclonal antibodies (McAbs) directed against CD34 antigen, have been extensively explored in different hematological malignancies. Accordingly, evidence progressively accumulated that reactivity for CD34 was almost exclusive to acute leukemia blast cells while absent in chronic mature disorders. Since then, CD34 expression has been included in most panels of McAbs used to characterize the immunophenotype of immature leukemic cells as a useful marker in discriminating between mature and immature hematopoietic leukemic cells. Cellular expression of CD34 plays a relevant role in acute leukemias and the CD34+ represents a heterogeneous group of leukemias characterized by varying clinical, genetic and biological features; its utility in defining specific disease subgroups requires combined assessment with other immunological markers. An effort towards the standardization of methods, reagents, and therapy protocols to be applied to de novo and secondary acute leukemias should be made to achieve comparability of results within and between different centers, as a basis for quality assurance and quality control programs.