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Soft Tissue Tumors
Round cell liposarcoma
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Reviewer: David Lucas, M.D., University of Michigan Health Systems (January 2009)
Revised: 22 October 2009, last major update June 2009
Definition
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● High grade tumor composed of small round or spindled cells with frequent mitotic figures
Terminology
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● Also called poorly differentiated myxoid liposarcoma
Treatment and prognosis
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● Aggressive, poor outcome if at least 5% of tumor is round cell (AJSP 1996;20:171)
● Frequently metastasizes to retroperitoneum, pleural cavity, soft tissue or pelvis; less often to lung
● Median survival 55 months (Ann Surg Oncol 2007;14:1507)
Case reports
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● 30 year old man with thigh mass (Case of the Week #10)
● 60 year old woman with retroperitoneal mass (Univ Pitt Case #302)
MRI images
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Thigh tumor
Gross description
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● Opaque white nodules, fleshy
Gross images
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Thigh tumor post-chemotherapy 44 year old woman with axillary tumor
(R-round cell component)
Micro description
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● Cellular areas of small, round or spindled cells with sparse eosinophilic and granular cytoplasm and large nuclei
● Scattered lipoblasts, frequent mitotic figures and necrosis
● Vasculature is less prominent than pure myxoid cases
● Frequent pseudoglandular tumor cells
● Often a transition between well differentiated myxoid and poorly differentiated round cell areas
● Note: classify as round cell if round cells comprise 5% or more of tumor volume
Micro images
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Sheets of primitive round cells
Small round cells are pleomorphic
Well-differentiated primary and poorly differentiated (round cell) metastasis
Transition between round cell and myxoid areas
Post-chemotherapy
Other images: small round tumor cells with minimal cytoplasm in myxoid stroma; perivascular pattern; invasion of fascia; pseudocystic cavity due to necrosis; branched capillaries in myxoid poor stroma; Alcian blue PAS stain
Cytology description
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● Hypercellular smears with single round cells with scant cytoplasm and naked nuclei
● Nuclei usually round, occasionally oval
● Variable background vacuoles, intracytoplasmic vacuoles, fragments of myxoid stroma with neoplastic cells
● No prominent pleomorphism (Cancer 2003;99:28)
Cytology images
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Tumor cells are round with uniform Most cells have single naked nuclei
chromatin and nucleoli (Pap) with round/oval shape (Diff-Quik)
Round tumor cells, occasional fragments Prominent cytoplasmic microvacuoles
of myxoid stroma and vascular structures and occasional lipoblast-like cells (Diff-Quik)
of myxoid liposarcoma (Diff-Quik)
Positive stains
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● CD31 and CD34 highlight vasculature; S100+ lipoblasts (30-50%)
Electron microscopy
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● Lipid vacuoles and massive proliferation of mitochondria (Acta Cytol 1992;36:722)
Molecular images
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● Characteristic t(12;16)(q13:p11)
Differential Diagnoses
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● Metastatic carcinoma - clinical history, keratin+ cells, may have more pleomorphism
● Melanoma - various histologic patterns, usually prominent nucleoli, S100+ tumor cells, HMB45+
● Lymphoma - positive for B (CD20, CD79a) or T cell (CD3, CD4) markers
● Ewing’s/PNET - neuroendocrine morphology, CD99+, translocations involving EWS gene
Additional references
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● AJSP 1996;20:1047, Cancer 1996;15;77:1450
End of Soft Tissue Tumors > Round cell liposarcoma of soft tissue
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