Myxoid liposarcoma

37 year old female presented with pain in the left knee and was incidentally discovered to have a mass in the anterior tibialis. The lesion was biopsied, diagnosed and she subsequently received preoperative radiation therapy followed by resection of the anterior tibialis muscle.

Cross sections reveal a yellow white, homogenous, well circumscribed mass deep within the muscle.

Microscopic sections reveal numerous atypical adipocytes suspended in a prominent myxoid stroma with ‘chicken wire’ capillary vasculature, characteristic of myxoid liposarcoma.

A focal area demonstrated numerous lipoblasts. No round cell component was identified in the lesion.

Myxoid liposarcomas represent more than 30% of all liposarcomas and is the second most common subtype of liposarcoma. The lesion represents 10% of all adult soft tissue tumors. It is believed that the more aggressive counterpart of the myxoid liposarcoma is that of the round cell liposarcoma, and that the spectrum ranges between the two entities.

The hallmark cytogenetics of these two entities is t(12;16) (q13;p11) which can be found in more than 90% of all cases. Reciprocal translocation t(12;16)(q13;p11) of myxoid-round cell liposarcoma, described about twenty years ago, results in a fusion gene consisting of the 5' part of the FUS (TLS) gene and the complete coding region of the CHOP gene. CHOP, acronym of C/EBP-Homologous protein, is also called DDIT3 which stands for DNA damage-induced transcript 3. The second translocation of myxoid liposarcoma is associated to t(12;22;20) (q13;q12;q11) chromosomal translocation, resulting in the fusion of the DDIT3 and EWS genes.

Contributed by Sonja Chen MD

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