Dedifferentiated liposarcoma

Last revised by Rohit Sharma on 27 Sep 2022

Dedifferentiated liposarcomas (DDLPS) are malignant adipocytic soft tissue neoplasms that have progressed from primary or recurrent atypical lipomatous tumors/well-differentiated liposarcomas and are characterized by a much higher rate of recurrence, metastasis in about one-fourth of the cases and a much higher overall mortality.

Dedifferentiated liposarcomas are the result of dedifferentiation of well-differentiated liposarcomas, happening in about 10%, and in most of cases coexists with the latter. Most commonly they occur in the 7th decade of life with women and men being equally affected. In the retroperitoneum, dedifferentiated liposarcomas account for most pleomorphic sarcomas 1-3.

The diagnosis of dedifferentiated liposarcoma is established by typical pathological features.

Diagnostic criteria according to the WHO classification of soft tissue and bone tumors (5thedition) 1:

  • a gradual or sudden transition from well-differentiated liposarcoma to non-lipogenic sarcoma (high or low grade)

The following histological criterion is desirable:

  • MDM2 expression or MDM2 gene amplification

The most common presentation is that of a large painless mass, which might be found incidentally 1,2.

If left untreated dedifferentiated liposarcoma will progress locally and can metastasize to distant organs 1.

Dedifferentiated liposarcomas are usually biphasic neoplasms characterized by features of any subtype of well-differentiated liposarcomas with more or less abrupt transitions to highly cellular regions of higher-grade spindle cell or pleomorphic non-fatty sarcoma-like tumor components 1-4.

Dedifferentiated liposarcomas most frequently involve the retroperitoneum and less frequently the deep soft tissue locations of the extremities and other body regions such as the head/neck region, the paratesticular area or the mediastinum 1-3.

Macroscopically dedifferentiated liposarcomas are usually large multinodular tumors with solid non-fatty tannish colored portions and lipomatous yellow parts with gradual or abrupt transition zones 1.

The microscopic appearance of dedifferentiated liposarcomas includes the following features 1,3:

Immunohistochemistry stains are usually positive for MDM2 and/or CDK4 1.

Genetically dedifferentiated liposarcomas show a significant overlap with atypical lipomatous tumors/well-differentiated liposarcomas and involve MDM2 nuclear gene amplification 1.

A common radiological feature of dedifferentiated liposarcomas is the coexistence of lipomatous and solid non-fatty components 1,2.

  • size >5 cm
  • nodular non-fatty tissue components >1 cm
  • more than 1/4 of solid non-fatty tissue in a lipomatous tumor
  • multinodular tumor margins

They might displace other organs or tissue.

Usually appears as multilobulated with areas of low echogenicity 2.

CT usually shows a fat tissue density mass with thick or nodular enhancing areas. Calcifications might be found 3.   

On MRI dedifferentiated liposarcomas will display a mass with fatty and juxtaposed non-fatty components. The non-fatty components appear heterogeneous with contrast enhancement 2,5.

  • T1: hypointense signal of the non-fatty component
  • T2: heterogeneous hyperintense signal of the non-fatty component
  • T1 C+ (Gd): enhancement of the solid non-fatty components

The radiological report should include a description of the following:

  • form, location and size
  • tumor margins
  • amount of non-adipose tissue

The management of dedifferentiated liposarcomas includes resection with a local recurrence of about 40% in local recurrence in nearly all cases of retroperitoneal tumors if patients are observed over a longer time period like 10-20 years 1. Distant metastases happen in 15-20% of the cases.

Mortality is about 28-30% after five years and much higher after a 10-20 year period 1.

Similar to well-differentiated liposarcomas the tumors are not particularly sensitive to radiotherapy or chemotherapy 3. There is an accelerated clinical course for a minority of patients.  Myogenic, especially rhabdo myoblastic differentiation seems to be associated with a worse outcome 1.

The type 'dedifferentiated liposarcoma' was first reported by the American pathologist Harry L Evans in 1979 4,6.

Conditions or tumors which can mimic the presentation and/or the appearance of include 1-5:

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