Advances in Myeloid Neoplasm Diagnosis and Classification
Robert P Hasserjian, Professor of Pathology, Massachusetts General Hospital and Harvard Medical School
Myeloid neoplasms are clonal bone marrow disorders defined by perturbed hematopoiesis, variable morphologic changes or maturation arrest in the bone marrow and blood, and recurrent genetic abnormalities. Their diagnosis and classification increasingly require complex integration of morphology, flow cytometry, and detailed genetic testing. Myelodysplastic syndromes/neoplasms (MDS) are particularly challenging, as they lie on the border between non-neoplastic clonal myeloid proliferations and acute myeloid leukemia (AML). Current dysplasia thresholds that separate MDS from other cytopenic conditions are imperfect; better-defined morphologic criteria and incorporation of genetic features may improve diagnostic specificity for MDS. Flow cytometric abnormalities can provide valuable supportive evidence for MDS and may become especially useful when morphology is borderline or suboptimal. Genetic findings are central to modern MDS classification, including SF3B1 mutation, del(5q), and bi-allelic TP53 alterations. Emerging MDS entities include those defined by DDX41 mutation and other recently discovered genetic clusters. MDS/myeloproliferative neoplasms such as chronic myelomonocytic leukemia (CMML) have a nuanced distinction from MDS. Although CMML is currently separated from MDS mainly based on the peripheral blood monocyte count, using a combination of morphology, flow cytometry, monocyte partitioning, and mutation profiles may provide a more accurate distinction. AML is already defined largely by genetic groups, and new emerging groups have been recently identified, including some that may predict responses to specific therapies. Future classification of myeloid neoplasms will be increasingly based on genetic features, while preserving essential clinical and morphologic information to meaningfully inform prognosis and guide therapy.

This session is an overview of recent advances in haematological malignancy molecular entities and evolving diagnostic techniques. It is not designed to be comprehensive but rather to provide a review of select topics for familiarity with newer terminology.