Definition
Synonyms
Round cell liposarcoma
Accounts for about one third of all liposarcomas.
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 life. Some cases present with multiple metastases.
The myxoid component is tan and gelatinous, the round cell component firm and white.
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.
Myxoid and round cell liposarcomas both show an identical t(12;22)(q13;q11-12) translocation.
myxofibrosarcoma
aggressive angiomyxoma
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.
This page last revised 29.6.2004.
©SMUHT/PW Bishop