Myelodysplastic/myeloproliferative neoplasm (MPN), unclassifiable (MDS/MPN-U), has clinical and morphologic features of both myelodysplastic syndrome (MDS) and myeloproliferative neoplasms (MPNs), and does not meet diagnostic criteria for any other specific entity within MDS, MPN, or MPN, including therapy-related myeloid neoplasms, and cases evolving from a prior MDS or MPN. Diagnostic criteria for MDS/MPN-U include, among other specifications, a platelet count of greater than or equal to 450 × 10E9/L associated with bone marrow megakaryocytic proliferation. We present the case of a young adult patient with a several-year reported history of cytopenias, found to have thrombocytosis and 5% circulating blasts. Surprisingly, his bone marrow biopsy demonstrated hypocellularity (10%), with 5% to 10% blasts, myeloid hypoplasia, minimal fibrosis, and focal megakaryocytic dyspoiesis but no hyperplasia. The constellation of morphologic and clinical features presents a challenging differential diagnosis between MDS/MPN-U and MDS with excess blasts (as well as thrombocytosis). Molecular testing interestingly demonstrated an SF3B1 mutation, although no increased ring sideroblasts were found by iron staining. Cases such as these may prove instructive in refining our understanding of the MDS/MPN category, as well as its relationship to myelodysplasia and the complex molecular genetic landscape underlying myeloid neoplasia.
Myeloid neoplasms with germline predisposition are an increasingly recognized category within the World Health Organization classification. Detection requires a high degree of suspicion, with mounting awareness of clinically silent phenotypes and heterogeneous presentations, challenging diagnostic and laboratory testing considerations, need for surveillance of disease progression, and unique concerns in donor selection for stem cell transplantation. We describe the case of a patient who presented as a teenager with thrombocytopenia and was later diagnosed with chronic myelomonocytic leukemia, with eventual transformation to acute myeloid leukemia, which has relapsed after stem cell transplantation. She was found to have short telomeres and a TERT mutation, in addition to numerous features suggestive of a germline predisposition syndrome. These findings have not been specifically associated with chronic myelomonocytic leukemia and raise interesting questions about the associations between myelodysplastic/myeloproliferative neoplasms, telomere biology disorders, and the roles of specific myeloid mutations as drivers of disease.
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