Clinical applications of CD34 + progenitor cell immunophenotyping in myelodysplastic neoplasms—The CytHem SMD French network experience

Myelodysplastic neoplasms (MDS) are clonal hematopoietic disorders characterized by ineffective hematopoiesis, peripheral cytopenias, and a risk of progression to acute myeloid leukemia. As the disease originates in hematopoietic stem and progenitor cells (HSPCs), flow cytometry (FCM) has emerged as a key approach to interrogate the bone marrow CD34+ compartment, providing complementary information to morphology, cytogenetics, and molecular studies. This review summarizes current knowledge on CD34+ cell alterations in MDS, structured around three main axes: quantitative abnormalities, immunophenotypic aberrancies, and disruption of progenitor architecture. Based on these complementary abnormalities, the French CytHem‐SMD working group has developed an integrated flow cytometric strategy combining established diagnostic scores with leukemic stem cell and progenitor architecture analyses. We present this approach and ongoing efforts to standardize its implementation across laboratories, and discuss future developments which are expected to further improve the reproducibility and clinical utility of CD34+ compartment assessment in MDS.