dedifferentiated liposarcomaA poorly-differentiated pleomorphic sarcoma which accounts for 10% of liposarcomas. It is a mixture of well-differentiated liposarcoma and a high-grade non-lipogenic sarcoma, an aggressive component. About 50% of retroperitoneal liposarcomas are dedifferentiated. 75% occur in the retroperitoneum; other sites include the extremities and paratesticular region. Dedifferentiated areas can be that of:
(1) High-grade pleomorphic sarcoma, which mimics what was once called pleomorphic malignant fibrous histiocytoma or fibrosarcoma, or
(2) Low-grade sarcoma, mimicking well-differentiated fibrosarcoma, low-grade myxofibrosarcoma or fibromatosis. Divergent differentiation occurs in 1/4 of cases and includes rhabdomyosarcomatous, leiomyosarcomatous, osteo-chondrosarcomatous or angiosarcomatous areas.
Legs (e.g., popliteal fossa and medial thigh), retroperitoneal, perirenal, mesenteric region, shoulder.
Despite their high-grade appearance, DDLs tend to be less aggressive than other types of high-grade pleomorphic sarcomas: local recurrence in 40%, metastases in 10%. Location is the single most important prognostic factor; retroperitoneal DDLs fare far worse than those located on the extremities.
Any high-grade or pleomorphic sarcoma should be considered, as well as metastatic poorly-differentiated carcinoma, melanoma, or lymphoma.
Ring or giant-marker chromosomes due to an amplification of chromosome 12q13-15, which results in the amplification of one or more genes in the region, including HMGA2, MDM2, SAS, GLI, CHOP, CDK4.