Myxoid/round Cell Liposarcoma Research Articles

Cytogenetic and molecular genetic analyses of liposarcoma and its soft tissue simulators: recognition of new variants and differential diagnosis.

Liposarcoma is one of the most common sarcomas of adults. Its differential diagnosis and accurate subclassification are often problematic; the latter is also important with regard to appropriate treatment and prognosis. We studied a series of 23 liposarcomas that had unusual or previously undescribed features and 10 liposarcoma simulators and correlated the morphologic, cytogenetic, and molecular genetic findings. We found that use of cytogenetic-molecular genetic techniques aids in the distinction between myxoid-round cell liposarcoma and their simulators, chondroid lipoma, myxoid spindle cell-pleomorphic lipoma, cellular intramuscular myxoma, and myxofibrosarcoma. Poorly differentiated forms of round cell liposarcoma lacking morphologic evidence of lipogenesis can also be diagnosed using these techniques; however, the techniques do not aid in distinguishing low-grade myxoid from high-grade round cell liposarcomas. This study also shows that retroperitoneal liposarcomas with myxoid liposarcoma-like zones are part of the morphologic spectrum of well-differentiated-dedifferentiated liposarcoma rather than true myxoid liposarcomas. Perhaps most importantly, our results provide the first molecular genetic evidence that true mixed liposarcomas (mixed well-differentiated and myxoid liposarcoma) do indeed exist. They also unequivocally demonstrate the existence of small, round cell variants of pleomorphic liposarcoma that closely simulate myxoid-round cell liposarcoma.

Long-term follow up of pure myxoid liposarcomas with special reference to local recurrence and progression to round cell lesions.

Myxoid and round cell liposarcomas cytogenetically share the t(12;16)(q13;p11) translocation, and represent a continuous morphological spectrum including pure myxoid liposarcoma (PML), mixed (myxoid/round cell) liposarcoma (MXL) and pure round cell liposarcoma (RCL). It has been documented that a critical amount of RC lesion in low-grade, MXL is associated with poor prognosis. The present long-term follow-up study examined the factors that influence the progression of PML to RCL and several other prognostic factors and compared the results with those of liposarcomas initially diagnosed as MXL. Using 34 primary PML and their local recurrences after curative resection, and two initially diagnosed MXL, the appearance of RC lesion in PML was examined, and the prognostic significance of the local recurrence rate (times/month), tumor size, infiltrative proliferation (defined as entrapping of striated muscle fibers in the tumor), tumor necrosis and mitotic figures. The follow-up period ranged from 19 to 378 months (mean, 173.4 months). Based on Cox's proportional hazards regression model, a recurrence rate >/= 0.01 in 24 PML with recurrences (P = 0.037) and the presence of infiltrative proliferation in 34 PML (P = 0.043) were significant independent factors associated with poor prognosis. Round cell lesions were detected in the last recurrences of two surviving PML. These results indicate that through their recurrence, PML might potentially become malignant, independent of the proportion of RC lesions in the tumor. The appearance of RC lesions in subsequent recurrences may indicate a progression from PML to MXL.