Soft tissue
Adipose tissue tumors
Liposarcoma
Myxoid pleomorphic liposarcoma
Author: Raul Perret, M.D., M.Sc.
Editorial Board Member: Farres Obeidin, M.D.
Deputy Editor-in-Chief: Borislav A. Alexiev, M.D.
Last author update: 20 April 2022
Last staff update: 25 April 2022
Copyright: 2019-2024, PathologyOutlines.com, Inc.
PubMed Search: Liposarcoma myxoid pleomorphic
Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Pathophysiology | Clinical features | Diagnosis | Radiology description | Prognostic factors | Case reports | Treatment | Gross description | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Negative stains | Molecular / cytogenetics description | Molecular / cytogenetics images | Sample pathology report | Differential diagnosis | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2Cite this page: Perret R. Myxoid pleomorphic liposarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuemyxoidpls.html. Accessed November 28th, 2024.
Definition / general
- Rare and aggressive variant of liposarcoma that predominantly affects young patients and shows hybrid morphological features of myxoid liposarcoma and pleomorphic liposarcoma
Essential features
- Aggressive soft tissue tumor with poor overall survival
- Frequently affects young patients (< 30 years old) but some cases occur in older adults
- Predominantly arises in the mediastinum
- Most cases consist of a variable mixture of myxoid liposarcoma and pleomorphic liposarcoma-like areas
- FUS / EWSR1-DDIT3 fusions and MDM2 amplification are absent
Terminology
- Pleomorphic myxoid liposarcoma
ICD coding
Epidemiology
- Frequently affects young patients (< 30 years old) but some cases occur in older adults (Mod Pathol 2021;34:2043, Am J Surg Pathol 2009;33:645)
- No clear gender predilection
- F > M in one series (Am J Surg Pathol 2009;33:645)
- M = F in another study (Mod Pathol 2021;34:2043)
Sites
- Predominantly arises in the mediastinum (Am J Surg Pathol 2009;33:645, Mod Pathol 2021;34:2043)
- Other, less frequent locations: head and neck, trunk and limbs (Mod Pathol 2021;34:2043)
Pathophysiology
- Losses of chromosome 13, including the RB1 loci, are frequent and have been postulated as an important hallmark in myxoid pleomorphic liposarcoma tumorigenesis (Histopathology 2016;69:141)
Clinical features
- Lesions are frequently large at initial diagnosis, probably due to the preference for mediastinal location and delayed development of symptoms (Am J Surg Pathol 2009;33:645, Mod Pathol 2021;34:2043)
- Patients may present with rapidly enlarging masses or pain (Histopathology 2016;69:141, Virchows Arch 2021;479:537)
- Cases associated with Li-Fraumeni syndrome have been reported (Int J Surg Pathol 2020;28:225, Pediatr Surg Int 2017;33:631, Virchows Arch 2021;479:537)
Diagnosis
- Imaging features are poorly characterized; diagnosis depends on histologic findings and molecular techniques (selected cases)
Radiology description
- Poorly characterized radiological findings (data restricted to isolated case reports)
- MRI: large deep mass with low signal on T1 and high signal on T2, favoring a myxoid component (Histopathology 2016;69:141)
Prognostic factors
- Aggressive soft tissue tumor with poor overall survival
- High rate of local recurrence (50% of cases) and metastatic dissemination (40 - 100% of cases) (Am J Surg Pathol 2009;33:645, Mod Pathol 2021;34:2043)
Case reports
- 15 year old girl with a perineal mass (Pediatr Surg Int 2017;33:631)
- 21 year old man with a large mass arising in the neck (J Clin Pathol 2014;67:834)
Treatment
- Complete surgical excision with negative margins is the only potentially curative treatment
- Specific target therapies are currently unavailable
- Utility of adjuvant therapies (chemotherapy or radiotherapy) is not well established (Am J Surg Pathol 2009;33:645, Mod Pathol 2021;34:2043)
- Rare associations with Li-Fraumeni syndrome warrant prudence when considering treatment with radiotherapy
Gross description
- Macroscopic findings are poorly characterized in the literature
- Large and grossly infiltrative, to nodular masses with a variably myxoid cut surface (Int J Surg Pathol 2020;28:225)
Microscopic (histologic) description
- Most cases consist of a variable mixture of myxoid liposarcoma and pleomorphic liposarcoma-like areas (Am J Surg Pathol 2009;33:645, Mod Pathol 2021;34:2043)
- Myxoid liposarcoma-like areas:
- Poorly to moderately cellular and composed of spindle cells with inconspicuous cytoplasm and round to oval hyperchromatic nuclei, embedded in a myxoid matrix with abundant ramified capillaries
- Nuclear atypia and pleomorphism are low but usually are more prominent than in classic myxoid liposarcoma
- Myxoid pools are frequently seen
- Pleomorphic liposarcoma-like areas:
- Highly cellular and composed predominantly of pleomorphic cells with irregular hyperchromatic nuclei
- Variable adipocytic differentiation (frequent lipoblasts)
- Mitotic activity is generally high and tumor necrosis is frequent
Microscopic (histologic) images
Contributed by Raul Perret, M.D., M.Sc.
Lobulated architecture
Mucin pools
Myxoid liposarcoma-like areas
Lipoblasts
High grade areas
RB1 loss
CD34 expression
Positive stains
Negative stains
- Rb: loss of expression is seen in most cases (Mod Pathol 2021;34:2043)
- MDM2 and CDK4 (Virchows Arch 2021;479:537)
Molecular / cytogenetics description
- Sarcoma with complex genomics characterized by structural chromosomal aberrations and monoallelic RB1 deletion (Histopathology 2016;69:141, Mod Pathol 2021;34:2043)
- Array comparative genomic hybridization (aCGH): frequently shows a distinctive genomic profile with whole chromosome gains (usually chromosomes 1, 6 - 8, 19 - 21 and X) and losses (2 - 5, 10 - 17 and 22) (Mod Pathol 2021;34:2043)
- Methylation profiling: myxoid pleomorphic liposarcoma and classic pleomorphic liposarcoma have overlapping profiles (suggesting that they are closely related) (Mod Pathol 2021;34:2043)
- KMT2D mutations reported in one case (Histopathology 2016;69:141)
- FUS / EWSR1-DDIT3 fusions are absent (Am J Surg Pathol 2009;33:645)
- MDM2 amplification is absent (Mod Pathol 2021;34:2043)
Molecular / cytogenetics images
Contributed by Raul Perret, M.D., M.Sc.
aCGH profile
Sample pathology report
- Mediastinal mass, excision:
- Myxoid pleomorphic liposarcoma (see comment)
- Comment: Microscopic examination shows a biphasic tumor comprising myxoid liposarcoma and pleomorphic liposarcoma-like areas. The myxoid liposarcoma-like areas contain small, poorly proliferative spindle cells with mildly pleomorphic hyperchromatic nuclei and rare univacuolated lipoblasts. The cells are dispersed in a myxoid background rich in ramified capillaries. The pleomorphic liposarcoma-like areas are densely cellular and made of sheets of pleomorphic cells (including lipoblasts) showing high mitotic activity and areas of necrosis.
- Immunohistochemically, the tumor cells are focally positive with CD34, negative with MDM2 and show loss of RB1 expression. FISH studies show the absence of DDIT3 rearrangement. Altogether, these findings support the above diagnosis of myxoid pleomorphic liposarcoma. This recently described sarcoma shows a high rate of local and distant spread (Am J Surg Pathol 2009;33:645, Mod Pathol 2021;34:2043).
Differential diagnosis
- Myxoid liposarcoma:
- Mainly occurs in the lower limb (Cancer 1996;77:1450)
- Spindle to ovoid cells embedded in a myxoid stroma with branching capillaries (Cancer 1996;77:1450)
- Nuclear pleomorphism is extremely rare (Cancer 1996;77:1450)
- FUS / EWSR1-DDIT3 fusions in virtually all cases (Diagn Mol Pathol 2011;20:218)
- Dedifferentiated liposarcoma:
- Generally, older adults (mean age > 60 years) (PLoS One 2021;16:e0246958)
- Most cases arise in the retroperitoneum and lower limbs, rarely in the mediastinum (Histopathology 2022;80:538)
- Can be rich in myxoid stroma (Histopathology 2013;62:287)
- Usually associated with a well differentiated component consisting of lobules of adipocytes with atypical (hyperchromatic nuclei) and hypercellular fibrous septa with atypical stromal cells
- MDM2 and CDK4 expression (Am J Surg Pathol 2005;29:1340)
- MDM2 amplification in virtually all cases (Am J Surg Pathol 2013;37:1259)
- Pleomorphic liposarcoma:
- Generally, older adults (mean age > 60 years) (PLoS One 2021;16:e0246958)
- In general, a typical myxoid liposarcoma-like component is absent (Mod Pathol 2021;34:2043)
- Rare cases can show myxofibrosarcoma-like areas, which may be hard to distinguish from myxoid pleomorphic liposarcoma (Am J Surg Pathol 2004;28:1257)
- Distinguishing from myxoid pleomorphic liposarcoma on morphology alone can be subjective but currently has no impact on management
- Atypical spindle cell / pleomorphic lipomatous tumor:
- Arises predominantly in the extremities (Am J Surg Pathol 2017;41:234)
- Mitotic activity is low and tumor necrosis is absent (Am J Surg Pathol 2017;41:234, Am J Surg Pathol 2017;41:1443)
- Usually a milder degree of nuclear atypia
- Ramified capillaries with a chicken wire pattern are rarely seen (Am J Surg Pathol 2017;41:1443)
- aCGH profiles are simpler and do not show whole chromosome gains and losses (Am J Surg Pathol 2017;41:1443)
Board review style question #1
A 25 year old man presented with a rapidly evolving mediastinal mass that shows lipomatous areas on MRI. Histology shows a richly vascular myxoid tumor with adipocytic and spindle cell components. Cellular density and nuclear pleomorphism are variable, ranging from low to high. Mitotic activity is brisk, and tumor necrosis is present. On immunohistochemistry, the tumor cells stain for CD34, show RB1 loss and negativity for MDM2. FISH analyses show no rearrangement of DDIT3. Which of the following is most likely the correct diagnosis?
- Atypical myxoid liposarcoma
- Atypical spindle cell / pleomorphic lipomatous tumor
- Dedifferentiated liposarcoma
- Myxoid pleomorphic liposarcoma
- Pleomorphic liposarcoma
Board review style answer #1
Board review style question #2
Which of the following is true about myxoid pleomorphic liposarcoma?
- It is an intermediate malignancy tumor
- It predominantly arises in children and young adults
- MDM2 amplification is present in a subset of cases
- Most cases are associated with Li-Fraumeni syndrome
- Most cases show DDIT3 gene rearrangements
Board review style answer #2
B. It predominantly arises in children and young adults
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Reference: Myxoid pleomorphic liposarcoma
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Reference: Myxoid pleomorphic liposarcoma
