Soft tissue

Adipose tissue tumors

Liposarcoma

Myxoid pleomorphic liposarcoma


Editorial Board Member: Farres Obeidin, M.D.
Deputy Editor-in-Chief: Borislav A. Alexiev, M.D.
Raul Perret, M.D., M.Sc.

Last author update: 20 April 2022
Last staff update: 25 April 2022

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PubMed Search: Liposarcoma myxoid pleomorphic

Raul Perret, M.D., M.Sc.
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Cite this page: Perret R. Myxoid pleomorphic liposarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuemyxoidpls.html. Accessed August 14th, 2022.
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
  • ICD-O: 8859/3 - myxoid pleomorphic liposarcoma
  • ICD-11:
    • 2B59.Y - liposarcoma, other specified primary site
    • XH3EL0 - myxoid liposarcoma
    • XH25R1 - pleomorphic liposarcoma
Epidemiology
Sites
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
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
Case reports
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

Negative stains
Molecular / cytogenetics description
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
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?

  1. Atypical myxoid liposarcoma
  2. Atypical spindle cell / pleomorphic lipomatous tumor
  3. Dedifferentiated liposarcoma
  4. Myxoid pleomorphic liposarcoma
  5. Pleomorphic liposarcoma
Board review style answer #1
D. Myxoid pleomorphic liposarcoma

Comment Here

Reference: Myxoid pleomorphic liposarcoma
Board review style question #2
Which of the following is true about myxoid pleomorphic liposarcoma?

  1. It is an intermediate malignancy tumor
  2. It predominantly arises in children and young adults
  3. MDM2 amplification is present in a subset of cases
  4. Most cases are associated with Li-Fraumeni syndrome
  5. Most cases show DDIT3 gene rearrangements
Board review style answer #2
B. It predominantly arises in children and young adults

Comment Here

Reference: Myxoid pleomorphic liposarcoma
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