Dedifferentiated liposarcoma

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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 ¼ of the cases and a much higher overall mortality.

Epidemiology

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

Clinical presentation

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

Complications

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

Pathology

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 .

Location

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

Macroscopic appearance

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 .

Microscopic appearance

The microscopic appearance of dedifferentiated liposarcomas includes the following features :

Immunohistochemistry

Immunohistochemistry stains are usually positive MDM2 and/or CDK4 .

Genetics

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

Radiographic features

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

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

They might displace other organs or tissue.

Ultrasound

Usually appears as multilobulated with areas of low echogenicity .

CT

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

MRI

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

  • 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

Radiology report

The radiological report should include a description of the following:

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

Treatment and prognosis

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

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

Similar to well-differentiated liposarcomas the tumors are not particularly sensitive to radiotherapy or chemotherapy .

Differential diagnosis

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

See also