• Leslie Naesens, Helena Devos, Friedel Nollet, Lucienne Michaux, and Dominik Selleslag.
• Department of Internal Medicine, University Hospital Ghent, Ghent, Belgium.
• Acta Haematol. 2018 Jan 1; 140 (2): 97-104.

IntroductionMyeloid sarcoma (MS), previously known as granulocytic sarcoma or chloroma, is a rare neoplastic condition defined as a tumor mass consisting of myeloblasts or immature myeloid cells occurring at an extramedullary site. Clinical presentation is diverse and determined by a tumor mass effect or local organ dysfunction.Case ReportWe report the case of a 25-year-old previously healthy male with rapidly progressive shortness of breath. A chest CT scan demonstrated a heterogenous anterosuperior mediastinal mass with pleural and pericardial invasion. A diagnosis of MS with both myeloid and lymphoid characteristics was made by pathologic, morphologic, and immunophenotypic investigation. Next generation analysis revealed a pathogenic TP53 mutation (c.1035_1036insCT, p.Glu346Leufs*25). After 4 cycles of chemotherapy only a partial metabolic response and tumor size reduction was obtained. A pretransplant bone marrow biopsy revealed the progression of disease to acute myeloid leukemia. Cytogenetic analysis demonstrated a t(10; 11)(p12;q21). Fluorescence in situ hybridization confirmed the presence of a PICALM-MLLT10 fusion gene.ConclusionMS with a mediastinal localization is rare and often misdiagnosed as malignant lymphoma. Acute leukemia harboring a PICALM-MLLT10 fusion gene is characterized by a mixed T cell and myeloid phenotype. The rearrangement is a rare recurrent translocation associated with specific clinical features, as illustrated in this case report.© 2018 S. Karger AG, Basel.

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