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 st udied a series of 23 liposarcomas that had unusual or previously undescribe d features and 10 liposarcoma simulators and correlated the morphologic, cy togenetic, 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 cel l-pleomorphic lipoma, cellular intramuscular myxoma, and myxofibrosarcoma. Poorly differentiated forms of round cell liposarcoma lacking morphologic e vidence of lipogenesis can also be diagnosed using these techniques; howeve r, the techniques do not aid in distinguishing low-grade myxoid from high-g rade round cell liposarcomas. This study also shows that retroperitoneal li posarcomas with myxoid liposarcoma-like zones are part of the morphologic s pectrum of well-differentiated-dedifferentiated liposarcoma rather than tru e myxoid liposarcomas. Perhaps most importantly, our results provide the fi rst molecular genetic evidence that true mixed liposarcomas (mixed well-dif ferentiated and myxoid liposarcoma) do indeed exist. They also unequivocall y demonstrate the existence of small, round cell variants of pleomorphic li posarcoma that closely simulate myxoid-round cell liposarcoma.