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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 stromaperivascular patterninvasion of fasciapseudocystic cavity due to necrosisbranched capillaries in myxoid poor stromaAlcian 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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