Myxoid liposarcoma

Definition

A malignant tumour composed of primitive mesenchymal cells and variable numbers of signet-ring cell like lipoblasts, with a branching vascular pattern.

Synonyms

Round cell liposarcoma

Epidemiology

Accounts for about one third of all liposarcomas.

Clinical features

Usually arises in the deep tissues of the thigh, rarely in the retroperitoneum or subcutaneously. Usually in young adults, it is the least uncommon form of liposarcoma in the first two decades of life1. Some cases present with multiple metastases.

Macroscopic appearances

The myxoid component is tan and gelatinous, the round cell component firm and white.

Histopathology

The tumour forms lobules, with increased cellularity at the edges of nodules. There is a component of small round or oval mesenchymal cells. Lipoblasts resemble small signet ring cells. There is a prominent myxoid stroma. Capillaries show a characteristic "chicken wire" branching pattern. Extracellular mucin may form microcystic pools. Giant cells and spindle cells are absent.

Some cases progress to a cellular round cell appearance. The cells vary from small to large and a myxoid stroma is lacking. The transition from the myxoid areas is often gradual.

Immunohistochemistry

Useful in round cell tumours, which are S-100 positive. A monoclonal antibody against the chimeric protein TLS/EWS-CHOP hold promise of specificity but more cases need to be studied.

Cytogenetics

Myxoid and round cell liposarcomas both show t(12;16)(q13;p11) or t(12;22)(q13;q11-12) translocations2,3.

Ultrastructure

Differential diagnosis

myxofibrosarcoma
myxoid chondrosarcoma
aggressive angiomyxoma

Management

Prognosis

Local recurrence is common. One third of cases develop distant metastases, including unusual sites such as retroperitoneum, axilla and bone. A round cell appearance occupying more than 5% of the tumour is associated with a worse prognosis. Multifocal tumours of any grade have a poor prognosis.

References

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

1 Alaggio R, Coffin CM, Weiss SW, et al. Liposarcomas in young patients: a study of 82 cases occurring in patients younger than 22 years of age. Am J Surg Pathol 2009; 33:645-58

2 Willeke F, Ridder R, Mechtersheimer G, Schwarzbach M, Duwe A, Weitz J, et al. Analysis of FUS-CHOP fusion transcripts in different types of soft tissue liposarcoma and their diagnostic implications. Clin Cancer Res. 1998 Jul;4(7):1779-84.

3 Willmore-Payne C, Holden J, Turner KC, Proia A, Layfield LJ. Translocations and amplifications of chromosome 12 in liposarcoma demonstrated by the LSI CHOP breakapart rearrangement probe. Arch Pathol Lab Med. 2008 Jun;132(6):952-7.

This page last revised 16.5.2009.