Soft tissue
Adipose tissue
Dedifferentiated liposarcoma

Author: Michael Clay, M.D. (see Authors page)

Revised: 28 December 2017, last major update December 2017

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Dedifferentiated liposarcoma[TI] free full text[sb]

Cite this page: Clay, M. Dedifferentiated liposarcoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/softtissuededifflipo.html. Accessed May 22nd, 2018.
Definition / general
  • Well differentiated liposarcoma (WDL) with transition, either in the primary tumor or as a recurrence, to a sarcoma that is typically nonlipogenic
  • Although historically considered to only be high grade, variable grading is now recognized in dedifferentiated liposarcoma (DDL)
Essential features
  • Nonlipogenic sarcoma (typically) that arises from well differentiated liposarcoma
    • Precursor well differentiated liposarcoma may or may not be identifiable in the background
  • Both low and high grade classifications are now recognized (see terminology below)
  • Molecularly characterized by ring or giant marker / rod chromosomes composed of material from 12q13-15
    • Results in localized amplification of several neighboring genes, including MDM2
  • Rarely, the high grade component can be lipogenic and resemble pleomorphic liposarcoma (homologous lipoblastic differentiation, Am J Surg Pathol 2010;34:1122)
  • First tumor to consider in a high grade sarcoma of the retroperitoneum in an adult
    • Retroperitoneal tumors historically regarded as inflammatory subtype of malignant fibrous histiocytoma (MFH) are now considered to represent a common morphologic pattern of dedifferentiation in dedifferentiated liposarcoma
Terminology
  • Although originally these tumors were all considered high grade, low grade dedifferentiation is now a recognized phenomenon
    • Low grade dedifferentiation can be histologically indistinguishable from cellular well differentiated liposarcoma; the terminology that is used varies among practicing pathologists
    • Although some report comparable prognosis for well differentiated and low grade dedifferentiated cases (Am J Surg Pathol 2007;31:1), others report an unfavorable outcome with any percentage or degree of dedifferentiation (Am J Surg Pathol 1997;21:271)
  • Minimal dedifferentiation: although controversial, some require macroscopic evidence of dedifferentiation (> 1.0 cm) to label a tumor as truly dedifferentiated
    • Even cases with so called minimal dedifferentiation (< 1.0 cm) can still carry an inferior prognosis when compared to well differentiated liposarcoma; prolonged clinical follow up is recommended regardless of size
Epidemiology
  • Typically occur in older adults, with a slight predilection for men
  • Occurs in up to 10% of well differentiated liposarcomas, with more frequent dedifferentiation noted in retroperitoneal primaries
Sites
  • Most common site is the retroperitoneum, followed by the extremities
  • Other frequent sites include the spermatic cord
  • Rare in the head and neck
  • Extremely rare in the subcutis; as a general rule, subcutaneous atypical lipomatous tumors do not dedifferentiate
Case reports
Prognosis and treatment
  • Better prognosis than other high grade pleomorphic sarcomas (Am J Surg Pathol 1994;18:1213) but still recurs in 40 - 75%, metastasizes in 10 - 15% and is associated with a 28% mortality rate (Am J Surg Pathol 1997;21:271)
  • Higher FNCLCC grade and myogenic differentiation are associated with worse clinical outcome (Am J Surg Pathol 2015;39:383)
  • Metastasis can occur in cases with low and high grade dedifferentiation and there is no minimal amount of dedifferentiation that mitigates this risk (Am J Surg Pathol 1997;21:271)
  • Cases with myxofibrosarcoma-like features are particularly aggressive (Mod Pathol 2005;18:976)
  • Retroperitoneal dedifferentiated liposarcoma has higher rates of local recurrence and disease specific death (Curr Opin Oncol 2011;23:373)
    • If followed long enough, nearly all retroperitoneal tumors will recur
  • Must rule out dedifferentiated liposarcoma in any retroperitoneal sarcoma. Can be aided by:
    1. Adequate sampling, particularly of peripheral areas
    2. Cytogenetics
    3. Immunostaining for MDM2 and CDK4 or molecular testing for 12q13-15 amplification
Clinical images

Images hosted on other servers:

Intraoperative image of axillary tumor

Gross description
  • Large firm mass (may resemble fish flesh) with coarse lobulation that can be surrounded by the more grossly fatty appearing well differentiated component
  • Dedifferentiation can be discrete and nodular or more gradual
  • Look for foci of necrosis in the high grade component
Gross images

Images hosted on other servers:

Various images

Microscopic (histologic) description
  • High grade dedifferentiated liposarcoma:
    • Well differentiated and dedifferentiated components are often both present and can have abrupt or gradual transitions
    • Dedifferentiated component is a cellular and typically a nonlipogenic sarcoma with significant pleomorphism
    • Although some propose a mitotic rate of > 5 mitoses/10 high power fields, this isn't uniformly adopted
    • Often resemble malignant fibrous histiocytoma (MFH, now referred to as undifferentiated pleomorphic sarcoma or UPS) with short fascicles of pleomorphic spindled cells associated with mixed inflammatory infiltrate
    • Can show a peculiar whirling pattern reminiscent of meningothelial structures (Histopathology 1998;33:414, Am J Surg Pathol 1998;22:945)
    • Heterologous elements in 5 - 10%
      • Heterologous elements can easily mislead pathologists in poorly sampled cases, especially in metastatic sites
      • Can manifest as neural differentiation, leiomyosarcoma, osteosarcoma / chondrosarcoma, rhabdomyosarcoma or pleomorphic liposarcoma (homologous lipoblastic dedifferentiation)
      • Rhabdomyoblastic differentiation has been associated with worse outcome
      • Angiosarcomatous differentiation has been reported (Virchows Arch 2005;446:456)
  • Low grade dedifferentiated liposarcoma:
    • Less common low grade tumor resembling fibromatosis or well differentiated fibrosarcoma
    • Nonlipogenic (in contrast to well differentiated spindle cell liposarcoma, which contains atypical fat / lipoblasts)
    • Considered by some to be the same as cellular atypical lipomatous tumor, although there is evidence even low grade dedifferentiation is associated with a poorer prognosis when compared to conventional atypical lipomatous tumor
    • Now a recognized WHO classification

Pitfalls and tips:
  • Look at the edges of dedifferentiated liposarcoma to identify a rim of background well differentiated liposarcoma that may mimic compressed background fat with reactive change
  • Dedifferentiated liposarcoma often shows a significant amount of heterogeneity (multiple patterns of differentiation and growth) and the confusing nature of the tumor can be a clue to the right diagnosis
  • Imaging may show both a fatty and solid nonfatty component
  • Metastases often contain only the dedifferentiated component
  • When in doubt use ancillary testing to confirm either protein overexpression or gene amplification
Microscopic (histologic) images

Images hosted on PathOut server:

Images contributed by Dr. Michael Clay - dedifferentiated liposaroma (DDL):

Low grade component

Delicate branching vasculature

High grade component with entrapped lipoblasts

Meningothelial-like whirls



Images from AFIP Soft tissue fascicle - Third series:

Dedifferentiated liposarcoma

Fibrosarcoma-like areas

Hemangioperi-cytoma type pattern

MFH-like areas

Neural appearance


Rhabdomyo-sarcomatous elements

Storiform pattern



Images hosted on other servers:

Various images

Osteosarcomatous differentiation

Fibrosarcoma-like


Leiomyosarcomatous differentiation in retroperitoneal tumor with hCG production

H&E and MDM2 staining



Malignant fibrous histiocytoma (MFH)-like areas

Paraganglioma-like pattern

Cytology description
  • Hypercellular with multinucleated, pleomorphic giant cells with abundant cytoplasm, small clusters of cells with high N/C ratio, spindled cells with elongated nuclei (Acta Cytol 2001;45:641)
  • Occasional osteoclast type giant cells (Cytojournal 2010;7:5)
  • Most samples are suitable for molecular confirmation
Cytology images

Images hosted on other servers:

FNAB of dedifferentiated liposarcoma

Positive stains
Molecular / cytogenetics description
Molecular / cytogenetics images

Images hosted on other servers:

FISH studies performed on FNA cell block sections of DDL

Differential diagnosis
  • Leiomyosarcoma:
    • Even in pleomorphic cases there are usually areas with morphology distinctive of well differentiated leiomyosarcoma
    • There is no background well differentiated liposarcomatous component and no 12q13-15 amplification
    • Immunostaining can be supportive but beware of desmin / actin expression in dedifferentiated liposarcoma
  • Malignant peripheral nerve sheath tumor (MPNST):
    • No well differentiated liposarcomatous component
    • History of neurofibromatosis can be helpful
    • Be wary of molecular / immunohistochemical testing as 20% of MPNST can have MDM2 gene amplification and protein overexpression
    • More commonly located in the deep soft tissues of the extremities than in the retroperitoneum
    • Typically more uniform in growth pattern than dedifferentiated liposarcoma, although the distinction may be very difficult
  • Melanoma:
    • Look for a clinical history of melanoma
    • Immunohistochemical staining can be informative with S100 being consistently positive, although other melanocytic markers are frequently negative (HMB45 and MelanA)
  • Pleomorphic liposarcoma (PLS):
    • Has lipoblasts set in the background of a pleomorphic sarcoma
    • Only way to distinguish PLS from dedifferentiated liposarcoma with secondary homologous differentiation is to either identify background well differentiated liposarcoma or verify MDM2 overexpression or amplification by ancillary studies (Cancer Cytopathol 2014;122:128)
      • This is an important distinction as pleomorphic liposarcoma has a significantly worse prognosis
  • Rhabdomyosarcoma:
    • No well differentiated liposarcomatous component, no 12q13-15 amplification or MDM2 protein overexpression
    • Rhabdomyoblastic stains can be unreliable given heterologous differentiation in dedifferentiated liposarcoma
  • Other sarcoma subtype infiltrating background adipose tissue:
    • Try to look in areas outside of the main tumor bulk to identify a well differentiated liposarcoma component, imaging can be particularly useful in showing a well differentiated fatty component associated with the higher grade sarcoma
    • Molecular and immunohistochemical studies are helpful
      • This may be particularly necessary when the background entrapped fat takes on a reactive appearance with fat necrosis, as this can closely mimic an underlying well differentiated liposarcoma
  • Sarcomatoid carcinoma:
    • Look for epithelial markers (EMA / cytokeratin) and clinical history indicative of a primary epithelial malignancy
    • No well differentiated liposarcomatous component, no 12q13-15 amplification
  • Sarcomatoid mesothelioma:
    • Similar age group but often have a clinical history of asbestos exposure, even in peritoneal disease (Am J Surg Pathol 2015;39:1568)
    • Variably positive for mesothelial markers (cytokeratin in 93%, calretinin only 31%; Mod Pathol 2010;23:470)
    • There is no well differentiated liposarcomatous component and no 12q13-15 amplification
  • Undifferentiated pleomorphic sarcoma (UPS) / malignant fibrous histiocytoma (MFH):
    • Retroperitoneal tumors are dedifferentiated liposarcoma until proven otherwise
      • Be very wary of this diagnosis in that location
    • Although UPS may have a complex karyotype, MDM2 gene amplification would indicate the diagnosis of dedifferentiated liposarcoma (Mod Pathol 2003;16:256)
Board review question #1
Which of the following is not associated with an adverse prognosis in patients with dedifferentiated liposarcoma?

  1. Advanced clinical stage
  2. Amount of the dedifferentiated component
  3. Heterologous differentiation into rhabdomyosarcoma
  4. Myxofibrosarcomatous morphology
  5. Retroperitoneal location
Board review answer #1
B. The amount of the dedifferentiated component is not associated with clinical outcome in patients with dedifferentiated liposarcoma.