Myeloid sarcoma (MS) is an extramedullary tumor of myeloid precursor cells, which can precede or occur concomitantly with acute myeloid leukemia, myelodysplastic syndrome, or myeloproliferative neoplasms. Although MS can involve any organ, it is more common in the central nervous system (CNS) and gonads, sites known as “pharmacologic sanctuaries” where leukemic cells can survive despite systemic chemotherapy. Less often, this tumor can be the manner of relapse after allogeneic bone marrow transplantation.
The diagnosis is based on morphology and immunophenotype by either flow cytometry or immunohistochemistry of paraffin-embedded tissue, and confirmed by FISH or molecular studies. Myeloid sarcomas usually express the leukocyte common antigens CD45, CD13, CD33, CD43 and lack T-cell and B-cell antigens
