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Soft Tissue Tumors

Adipose tissue

Liposarcomas of soft tissue - general

Reviewer: Vijay Shankar, M.D. (see Reviewers page)
Revised: 11 November 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

General
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● Most common soft tissue sarcoma of adults (20%)
● See also discussion in Breast-malignant, Heart-tumor, Liver-tumor, Oral Cavity, Pleura and Testis chapters

Epidemiology
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● Age 40+ years
● Most cases in children are actually lipoblastoma or giant cell fibroblastoma
● Rarely associated with multiple benign lipomas

Sites
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● Deep soft tissue (thigh, retroperitoneum, popliteal fossa)
● Mediastinum is uncommon (Am J Surg Pathol 2007;31:1868)
● Head and neck cases are often initially misdiagnosed, 53% recur (Head Neck 2009;31:28)
● Usually NOT superficial, NOT intramuscular, NOT in neck

Treatment and prognosis
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● Tumor size and histologic classification are important prognostic factors
● Surgery still remains the mainstay of treatment and the only approach offering the potential of cure
● Postoperative radiation reduces recurrence rate
● 10 year local recurrence-free and metastasis-free survival in low-grade group is 87% and 95%, and in high-grade group is 75% and 61% (Cancer 2008;113:1649)

Gross description
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● Large, well circumscribed but not encapsulated
● Mimics myxoma, lipoma and cerebral convolutions

Micro description
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● Per WHO (20020, composed of three subtypes:
  (1) well-differentiated and dedifferentiated liposarcoma (WDLPS/DDLPS)
  (2) myxoid and round cell liposarcoma (MLS and RCL)
  (3) pleomorphic liposarcoma (PLS)
● Lipoblasts are relatively specific, resemble fetal fat cells, and are somewhat smaller than mature adipocytes
● Lipoblasts have round, sharply demarcated cytoplasmic lipid (clear) vacuoles which scallop the nucleus and are smaller than vacuoles of mature adipocytes; spikes of chromatin may project between the vacuoles; may resemble signet ring cells or have central nuclei with small indentations by multiple fat vacuoles

Positive stains
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● S100 (often), calretinin (Hum Pathol 2006;37:312)

Electron microscopy description
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● Lipoblasts resemble brown fat cells; are multivacuolated with lipid droplets, micropinocytotic vesicles, glycogen, external lamina, intermediate filaments, Golgi, rough and smooth endoplasmic reticulum, mitochondria
● Lipoblasts frequently are close to capillaries and pericytes
● Also lipid-free, poorly differentiated mesenchymal cells (Am J Clin Pathol 1986;85:649)

Differential diagnosis
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● Clear cell melanoma: strong S100+, HMB45+
● Fat necrosis: histiocytes are often circumferential around lipid droplets, associated with trauma, have central nucleus which is not deformed
● Infiltration of fat by nonfatty tumors: fat cells are normal size and at periphery of lesion
● Inflammatory lipoma
● Intramuscular myxoma
● Lipoblastoma / lipoblastomatosis
● Lipogranuloma
● Localized lipoatrophy: insulin injection sites
● Metastatic signet ring cell carcinoma: infiltrative, cytokeratin+, mucin+
● Pleomorphic / spindle cell lipoma
● Silicon granuloma (image)

Additional references
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● eMedicine #1; #2

End of Soft Tissue Tumors > Adipose tissue > Liposarcomas of soft tissue - general

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