Abstract / Summary
Abstract Background Myeloid sarcoma is an uncommon extramedullary manifestation of a myeloid neoplasm that may occur concurrently with acute myeloid leukemia (AML) or precede clinically recognized marrow disease. Its variable clinical and histopathologic appearance can result in diagnostic confusion, particularly when presenting as an isolated-appearing soft-tissue lesion in children. Case Presentation: A 7-year-old boy presented with fever, generalized petechiae and purpura, weakness, severe pancytopenia, and a recurrent painful left-forearm mass. The lesion had first appeared approximately 18 months earlier and was initially considered a hemangioma on ultrasonography. Subsequent histopathologic examination and a limited immunohistochemical panel suggested a lymphoproliferative disorder and later probable precursor lymphoblastic lymphoma. Following development of overt marrow disease, bone-marrow examination demonstrated 40% blasts, while flow cytometry supported AML with aberrant CD7 expression. Re-evaluation of the forearm specimen using a broader immunohistochemical panel demonstrated weak myeloperoxidase, CD7, CD117, and CD99 expression, resulting in reclassification as myeloid sarcoma. Treatment with daunorubicin, cytarabine, and thioguanine was initiated. Gemtuzumab ozogamicin was not administered because of low CD33 expression. Following the first induction course, the patient achieved remission with undetectable measurable residual disease by next-generation flow cytometry. Conclusion Persistent or recurrent pediatric soft-tissue lesions with atypical clinical behavior require adequate tissue sampling, broad lineage-directed immunophenotyping, and timely correlation with marrow findings. This case illustrates how myeloid sarcoma can precede clinically recognized AML and mimic both benign vascular and lymphoid lesions, while also demonstrating a favorable early response to AML-directed systemic therapy.