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Soft Tissue Tumors
Liposarcomas of soft tissue - general
Author: Nat Pernick, M.D., PathologyOutlines.com, Inc.
Reviewer: David Lucas, M.D., University of Michigan Health Systems (January 2009)
Revised: 26 June 2009, last major update June 2009
Definition
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● Most common soft tissue sarcoma of adults (20%)
● See also discussion in Breast-tumor, 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 (AJSP 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
● 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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● Lipoblasts are relatively specific, resemble fetal fat cells, and are somewhat smaller than mature adipocytes
● 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 Path 2006;37:312)
Electron microscopy
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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 (AJCP 1986;85:649)
Differential Diagnoses
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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
● Intramuscular myxoma
● Localized lipoatrophy - insulin injection sites
● Lipoblastoma / lipoblastomatosis
● Lipogranuloma
● Metastatic signet ring cell carcinoma - infiltrative, cytokeratin+, mucin+
● Silicon granuloma (image)
● Spindle cell / pleomorphic lipoma, inflammatory lipoma
Additional references
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● eMedicine #1; #2
End of Soft Tissue Tumors > Liposarcomas of soft tissue - general
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