Track: Case Reports

Abstract:

Myeloid sarcoma is an uncommon extramedullary manifestation of acute myeloid leukemia (AML) that can pose significant diagnostic challenges, particularly when involving uncommon sites or exhibiting aberrant immunophenotypes. We report an adult male with a history of diffuse large B-cell lymphoma treated with chemotherapy, who subsequently developed therapy-related myelodysplastic syndrome progressing to AML. The patient presented with concurrent cutaneous and oral lesions. Histopathologic examination revealed sheets of medium-sized, slightly pleomorphic cells with open chromatin and prominent nucleoli. Immunohistochemistry identified an immature myeloid lineage (CD34, CD117, and myeloperoxidase positivity) with aberrant co-expression of T-cell antigens CD5 and CD7. Molecular testing identified TP53 and IDH1 mutations. The presence of both myeloid and T-cell marker expression raises a differential diagnosis of either a myeloid or T-cell neoplasm with aberrant markers or a T/myeloid mixed-phenotype acute leukemia (MPAL-T/M). This case underscores the heterogeneity of myeloid sarcoma in the skin and the risk of confusing it with cutaneous T-cell lymphomas if there is aberrant T-cell marker expression. A comprehensive immunophenotypic and molecular panel is needed to classify it accurately and to inform treatment in the setting of mixed features.

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Cody Thomas