Overview of Myelodysplastic/Myeloproliferative Neoplasms

Kathryn Foucar, MD

Blood smear from a patient with MDS/MPN shows marked leukocytosis with left shift. The patient also has a moderate anemia, while the platelet count is preserved. Note dysplastic neutrophils

Marked dysplastic features of neutrophils are evident in this peripheral blood smear from a patient with MDS/MPN. Note the nuclear segmentation abnormalities and hypogranularity of the neutrophil

TERMINOLOGY

Abbreviations

Myelodysplastic/myeloproliferative neoplasms (MDS/MPN)

Definitions

De novo clonal chronic myeloid neoplasm characterized by hybrid myelodysplastic and myeloproliferative features manifested by at least 1 cytopenia and at least 1 cytosis in blood
Maturation is intact, mature cells predominate
Blasts and blast equivalents are < 20% in blood and bone marrow
Multiple subtypes defined with specific criteria

WHO 2008 Classification of MDS/MPN

Chronic myelomonocytic leukemia (CMML)
Atypical chronic myeloid leukemia, BCR-ABL1 negative (aCML)
Juvenile myelomonocytic leukemia (JMML)
Myelodysplastic/myeloproliferative neoplasm, unclassifiable (MDS/MPN-U)
Refractory anemia with ring sideroblasts and thrombocytosis (RARS-T) (provisional category)

ETIOLOGY/PATHOGENESIS

Molecular Genetic Findings

No disease defining molecular/cytogenetic features
Aberrations in RAS/MAPK signaling pathways common and linked to abnormal cell proliferation
- May include mutations in PTNPN11, NRAS, KRAS, or NF1 most notably in JMML
Many exclusionary genetic findings including absence of BCR-ABL1, PDGFRA/B, FGFR1 mutations, isolated del(5q), inv3(q21q26), and AML-defining translocations
- All of these mutations are pathogenetically linked to other types of myeloid neoplasms