An Unusual Case Of Disseminated Histiocytic Sarcoma Preceded By Myeloid Sarcoma With Concomitant Acute Myeloid Leukemia

Introduction/Objective Histiocytic sarcoma (HS) is rare (<1% of hematolymphoid neoplasms), and can present extranodally as disseminated disease. Immunophenotypically, the cells express CD163, CD68, lysozyme and CD45. HS often occurs as a secondary event following B-cell lymphomas, acute lymphoblastic leukemia or acute myeloid leukemia (AML) typically with monocytic differentiation retaining the same molecular/cytogenetic abnormalities as the primary tumor. Results Our patient, a 47 year old male was diagnosed with myeloid sarcoma (MS) following FNA of a new neck mass. A bone marrow biopsy revealed AML without monocytic differentiation. Flow cytometric findings of both marrow and neck mass were similar (positive for CD34, CD117, CD33, CD11b, CD13, CD15, CD64, CD7; negative for CD4, CD14, CD56). Karyotypic and FLT3 ITD mutation analysis were normal. CNS involvement was diagnosed 2 months later, while a marrow biopsy (status post therapy) confirmed resolution of AML. A hypermetabolic left perinephric mass noted by PET CT, when biopsied, showed large epithelioid polygonal cells with amphophilic cytoplasm and atypical vesicular nuclei (positive for CD68, PU.1; negative for LCA, CD163, CD34, CD4, pankeratin). A diagnosis of atypical epithelioid neoplasm suggestive of HS was rendered, although negativity for LCA and CD163 was unusual. No treatment was given for HS. A month later, the patient presented with a cheek mass diagnosed again as being suggestive of HS. His AML also relapsed. Next-generation sequencing (37 genes including BRAF) from both marrow and tissue samples detected the presence of a nonsense mutation in exon 7 of WT1 (p.Ser169). Conclusion Our case appears to be the first reported one of disseminated HS preceded by MS and concomitant AML, lacking monocytic differentiation. The findings overall support the hypothesis of origin as being from a common progenitor cell differentiating along both myeloid and histiocytic/other cell lineages at different time points.