Myeloid sarcoma: A clinicopathological study with emphasis on diagnostic difficulties

Background: Myeloid sarcoma (MS) is a rare tumor composed of proliferation of myeloid precursors at extramedullary sites. They can arise de-novo or in association with hematological malignancies, most commonly acute myeloid leukemia. Clinically, it can masquerade as an abscess, cutaneous ulcer, or mass lesion. Morphologically, MS can mimic a variety of small round cell tumors including lymphomas and rhabdomyosarcoma. Aims: (1) To study the clinical presentations and laboratory findings in patients with MS; (2) to revisit the histomorphological findings and the differential diagnosis of MS; (3) to evaluate the diagnostic role of immunohistochemistry (IHC) and determine the useful markers for accurate diagnosis of MS. Materials and Methods: We reviewed cases of MS reported in our institution over a 10-year period from January 2004 to December 2013. The clinical presentations, laboratory data, and histopathological and immunohistochemical findings were studied. Results: There were nine cases in our database, none of which were clinically suspected to be MS. Age ranged from 3 to 55 years, with a slight female preponderance. Cervical lymph nodes were the most common site involved. Histologically, the common finding was the presence of medium- to large-sized cells with fine granular chromatin, small nucleolus, and scant cytoplasm along with scattered eosinophil precursors. Myeloperoxidase was the most useful IHC marker. All cases were also positive for leukocyte common antigen contributing to the diagnostic confusion with lymphoma. Conclusion: The possibility of MS should be considered when dealing with unusual lymphoma-like neoplasms that cannot be categorized as any of the Non-Hodgkin lymphoma subtypes.