Dedifferentiated liposarcoma

Definition

A malignant tumour consisting of both well differentiated liposarcoma and a transformed non-lipogenic component.

Epidemiology

Dedifferentiation is much more common in retroperitoneal well differentiated liposarcoma than in those occurring in the limbs. 90% of cases are primary, 10% of instances of dedifferentiation occur in recurrences.

Radiology

Imaging shows both lipomatous and non-lipomatous components.

Macroscopic appearances

Usually a fatty tumour with discrete solid non-fatty dedifferentiated areas.

Histopathology

The transition from well differentiated liposarcoma to dedifferentiated areas is usually abrupt but may be gradual. The atypical lipomatous component may be conventional or cellular. The dedifferentiated component is usually high grade, MFH-like pleomorphic sarcoma or myxofibrosarcoma. Less often the dedifferentiated areas are low grade non-lipogenic tumour. The non-lipogenic component has a mitotic rate of at least 5 per 10 HPF1. Heterologous elements include myosarcomatous, osteosarcomatous, chondrosarcomatous, paraganglioma-like1 and angiosarcomatous components and are present in 5-10% of cases. A meningiothelial-like concentric pattern has been described, associated with ossification.

Immunohistochemistry

MDM2 and CDK4 are positive.

Various antibodies identify heterologous elements.

Cytogenetics

There are ring or giant marker chromosome, as seen in well differentiated liposarcoma. The complex karyotypic abnormalities seen in pleomorphic liposarcoma are not seen.

Differential diagnosis

• High grade sarcomas not arising by dedifferentiation of liposarcoma:

  • fibrosarcoma

  • malignant peripheral nerve sheath tumour

  • malignant fibrous histiocytoma: inflammatory MFH is now thought to be a variant of dedifferentiated liposarcoma.

• if there is a heterologous component:

  • leiomyosarcoma

  • rhabdomyosarcoma

  • chondrosarcoma

  • osteosarcoma

Prognosis

The prognosis is better than that for other high grade sarcomas. Overall, 40% recur locally, but almost all retroperitoneal cases eventually recur. 15-20% show distant metastases, most often to lungs, but also to liver and other sites. The extent of the dedifferentiated areas and the presence of heterologous elements does not affect prognosis. The prognostic significance of microscopic foci of dedifferentiation is uncertain. Dedifferentiated liposarcoma may recur as well differentiated liposarcoma1.

References

World Health Organization Classification of Tumours, Tumours of Soft Tissues and Bone, IARC Press 2002.

1 Evans HL Atypical lipomatous tumor, its variants, and its combined forms: a study of 61 cases, with a minimum follow-up of 10 years. Am J Surg Pathol 2007; 31:1-14

This page last revised 25.5.2007.

©SMUHT/PW Bishop