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Myeloid Sarcoma : Differential

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Differential Diagnosis of Myeloid Sarcoma: Myeloid sarcoma is frequently misdiagnosed because it can mimic primary or metastatic carcinomas, melanomas, and hematopoietic malignancies such as diffuse large B-cell lymphoma, lymphoblastic lymphoma, blastic mantle cell lymphoma, and Burkitt lymphoma. In cutaneous myeloid sarcoma, the greatest histologic overlap is with blastic plasmacytoid dendritic cell neoplasm.

The presence of erythroid precursors, megakaryocytes, or eosinophilic myelocytes favors a myeloid origin. Myeloid sarcoma shows finely stippled nuclear chromatin and high mitotic activity. The presence of chromatin clearing and prominent nucleoli favor diffuse large B-cell lymphoma. However, immunophenotyping is essential for accurate diagnosis.

Caution: Myeloid sarcomas may show aberrant expression of B- and T-cell antigens. Cases with t(8;21)(q22;q22.1) and aberrant B-lineage marker expression (e.g. CD19, PAX5) may lead to an incorrect diagnosis of B-cell lymphoma. Similarly, cases with inv(16)(p13.1;q22) or t(16;16)(p13.1;q22) and aberrant expression of CD2 may be mistaken for T-cell lymphoma.

Expression of CD7 and CD56 alone should not be used as a basis for diagnosing T-cell or NK-cell lymphoma as these markers are frequently expressed in myeloid sarcomas. Myeloid sarcomas (megakaryocytic) with t(1;22)(p13.3;q13.1) often show clustering of tumor cells and mimic small blue round cell tumors of childhood. They are usually myeloperoxidase negative but positive for CD41 and CD61.

Leukemic infiltrates in tissues of AML patients should not be over-interpreted as myeloid sarcoma. The latter term is used only if they form space-occupying lesions with disruption of native tissue architecture.

Acute febrile neutrophilic dermatosis (Sweet's syndrome) may occur in patients with AML. There is dermal edema and a dermal infiltrate composed of mature neutrophils. It should not be over-diagnosed as myeloid sarcoma.

The image shows megakaryoblastic myeloid sarcoma presenting in the small intestine. Uniform cells with little cytoplasm form sheet-like growth effacing the normal architecture. The tumor cells were positive for CD34, CD43, myeloperoxidase, and CD61 by immunohistochemistry.

Image courtesy of: The New York Pathological Society (@NYPathSociety); used with permission.

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