Cytopathology of myeloid sarcoma: a study of 16 cases

The diagnosis of myeloid sarcoma (MS) in cytology samples is challenging, especially when these tumors occur prior to a diagnosis of acute myeloid leukemia. The aim of this study was to review our cytopathology service's experience with a series of MS cases.

Archival records were searched from which 16 cytology cases of MS were identified and reviewed. Clinical findings, cytomorphology, and ancillary studies were analyzed.

MS was secondary to acute myeloid leukemia in 14 cases, chronic myeloid leukemia (CML) in blast crisis in 1 case, and myelodysplastic syndrome in another. Flow cytometry was supportive in 11 cases, immunostains were helpful when performed in 4 cases, and fluorescence in-situ hybridization in the CML case showed t(9;22). Cellularity was variable in all leukemia subtypes. Blasts had round or cleaved nuclei with indistinct nucleoli. Maturing granulocytes were present only in the patient with CML, or with peripheral blood contamination (4 cases). Other blood precursors were absent. Apoptosis and lymphoglandular bodies were present in almost one-half of the cases, which correlated with increased blasts. Mitoses were infrequent (6 cases) and necrosis was not seen.

The diagnosis of MS in cytology specimens can be made in cases with adequate cellularity and supportive ancillary studies in the correct clinical context. MS was harder to diagnose in cytology cases with low cellularity, blood contamination, and few blasts. Cytologic features that pose diagnostic pitfalls are lymphoglandular bodies suggestive of lymphoma and maturing or mixed granulocytes that mimic infection.