Soft Tissue Tumors - Round cell liposarcoma

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Soft Tissue Tumors

Adipose tissue-liposarcoma

Round cell liposarcoma

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 14 November 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● High grade tumor composed of small round or spindled cells with frequent mitotic figures
● 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 (Am J Surg Pathol 1996;20:171, Cancer 1996;77:1450)
● 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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● 28 year old man with painful subcutaneous mass on flank (Ann Dermatol 2011;23:338)
● 30 year old man with thigh mass (Case of the Week #10)
● 60 year old woman with retroperitoneal mass (University of Pittsburgh)
● Young adult with scrotal swelling (J Med Assoc Thai 2005;88:1302)

Clinical images
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Various images

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; may resemble lymphoma or other round cell tumors
● Scattered lipoblasts, frequent mitotic figures and necrosis
● Frequent pseudoglandular tumor cells
● Vasculature is less prominent than pure myxoid cases
● Often a transition between well differentiated myxoid and poorly differentiated round cell areas
● Note: classify as round cell if 5% or more of tumor volume

Micro images
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Various images

Sheets of primitive round cells

Small round cells are pleomorphic

Comparison of well differentiated and poorly differentiated (round cell) tumors

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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Various images

Positive stains
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● CD31 and CD34 highlight vasculature
● S100+ lipoblasts (30-50%)

Electron microscopy description
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● Lipid vacuoles and massive proliferation of mitochondria (Acta Cytol 1992;36:722)

Molecular description
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● Characteristic t(12;16)(q13:p11) (Am J Surg Pathol 1996;20:1047)
● Activation of the PI3K/Akt pathway via activating mutation of PIK3CA, loss of PTEN, or IGF1R expression have a role in round cell transformation (Mod Pathol 2012;25:212)

Differential diagnosis
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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

End of Soft Tissue Tumors > Adipose tissue-liposarcoma > Round cell liposarcoma

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