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Myeloid sarcoma (MS) is defined in the World Health Organization classification as a tumor mass consisting of myeloblasts with or without maturation and involving any anatomic site other than the bone marrow. We present a case of MS developing in a patient with 5q- myelodysplastic syndrome (MDS) and review the relevant literature.A 77-year-old woman with recent diagnosis of MDS associated with del(5q) presented with symptoms and signs attributable to a mass involving the T8 vertebra. Biopsy of the spinal mass was performed and the specimen was analyzed using routine hematoxylin-eosin stain, immunohistochemical methods, and fluorescence in situ hybridization (FISH).Microscopic examination revealed an infiltrate of intermediate-large cells with basophilic cytoplasm and nuclei containing occasional prominent nucleoli. Immunohistochemical analysis showed that the neoplastic cells were positive for CD4, CD43, CD45, CD68, and CD117, and negative for B- and T-cell antigens supporting the diagnosis of MS. Fluorescence in situ hybridization of the spinal mass showed del(5q) in the neoplastic cells.Although the 5q- syndrome is a clinically indolent form of MDS, a small subset of patients may develop MS as illustrated in this patient. The relevant literature is also reviewed.