Extensive myeloid sarcoma presenting with esophageal compression and dysphagia as the initial manifestation.

RATIONALE: Myeloid sarcoma (MS) is an extramedullary tumor of immature myeloid cells that can precede or accompany acute myeloid leukemia (AML). Mediastinal/retroperitoneal involvement causing esophageal compression is rare and prone to misdiagnosis. PATIENT CONCERNS: A 67-year-old woman presented with 20 days of progressive dysphagia. DIAGNOSES: Contrast-enhanced Computed tomography showed infiltrative soft-tissue masses in the posterior mediastinum, para-aortic region, and bilateral chest/abdominal walls, encasing the esophagus and major vessels; endoscopy confirmed extrinsic esophageal stenosis. EUS-FNA was nondiagnostic for small-cell carcinoma. Core biopsy with high-power review revealed predominantly medium-to-large blasts with focal granulocytic maturation. Immunophenotype supported myeloid lineage: MPO diffuse positive; CD117 positive; focal CD34 and CD99; weak-to-focal CD45/LCA; negative B-cell (CD19, CD20, CD79a), T-cell (CD2, CD3, CD5, CD7), and epithelial markers (CK AE1/AE3, CK19). Ki-67 proliferation rate was 40%-50%. Peripheral blood counts were unremarkable for blasts or cytopenias; bone marrow aspirate/biopsy/flow showed no diagnostic evidence of AML. Final diagnosis: MS with extrinsic esophageal compression. INTERVENTIONS: AML-type systemic chemotherapy with the HAA regimen (homoharringtonine 3 mg d1-7, aclarubicin 20 mg d1-7, cytarabine 0.2 g d1-7; q3 weeks) plus standard supportive care. OUTCOMES: Dysphagia improved during the first cycle. Interval imaging demonstrated reduction of mediastinal/retroperitoneal soft-tissue bulk and improved esophageal lumen consistent with disease control. No radiotherapy or esophageal stenting was required. On follow-up, disease remained controlled without transformation to AML. LESSONS: Infiltrative mediastinal/retroperitoneal MS may present with esophageal obstruction and mimic lymphoma or carcinoma. High-index suspicion, targeted biopsy with high-power morphology, and a focused immunohistochemical panel are critical for timely diagnosis and treatment initiation.