The myelodysplastic syndromes (MDS) are a collection of myeloid malignancies characterized by one or more peripheral blood cytopenias. MDS are diagnosed in slightly more than 10,000 people in the United States yearly, for an annual age-adjusted incidence rate of approximately 4.4 to 4.6 cases per 100,000 people. They are more common in men and whites. The syndromes may arise de novo or secondarily after treatment with chemotherapy and/or radiation therapy for other cancers or, rarely, after environmental exposures.
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Prognosis is directly related to the number of bone marrow blast cells, to certain cytogenetic abnormalities, and to the amount of peripheral blood cytopenias. By convention, MDS are reclassified as acute myeloid leukemia (AML) with myelodysplastic features when blood or bone marrow blasts reach or exceed 20%. Many patients succumb to complications of cytopenias before progression to this stage. (Refer to the Pathologic and Prognostic Systems for Myelodysplastic Syndromes section of this summary for more information.) The acute leukemic phase is less responsive to chemotherapy than is de novo AML.
MDS are characterized by abnormal bone marrow and blood cell morphology. Megaloblastoid erythroid hyperplasia with macrocytic anemia, associated with normal vitamin B12 and folate levels, is frequently observed. Circulating granulocytes are often hypogranular or hypergranular, and may display the acquired pseudo-Pelger-Huët abnormality. Early, abnormal myeloid progenitors are identified in the marrow in varying percentages. Abnormally small megakaryocytes (micromegakaryocytes) may be seen in the marrow and hypogranular or giant platelets may appear in the blood.
MDS occur predominantly in older patients (usually those older than 60 years), with a median age at diagnosis of approximately 70 years, although patients as young as 2 years have been reported. Anemia, bleeding, easy bruising, and fatigue are common initial findings. (Refer to the PDQ summary on Fatigue for more information.) Splenomegaly or hepatosplenomegaly may indicate an overlapping myeloproliferative neoplasm. Approximately 50% of patients have a detectable cytogenetic abnormality, most commonly a deletion of all or part of chromosome 5 or 7, or trisomy 8. Single-nucleotide polymorphism array technology may increase the detection of genetic abnormalities to 80%.[4,5] Although the bone marrow is usually hypercellular at diagnosis, 10% of patients present with a hypoplastic bone marrow. Hypoplastic myelodysplastic patients tend to have profound cytopenias and may respond more frequently to immunosuppressive therapy.