Contributor: Gordon K. Klintworth
The myxoid liposarcoma is highly malignant neoplasm common soft tissue sarcoma composed of lipoblasts in various stages of differentiation. This variant of  liposarcoma, which is believed to arise from primitive mesenchymal cells, rather than from mature adipose connective tissue occurs most often in the thigh and retroperitoneum. Rarely it arises in the orbit. The tumor has a nodular growth pattern. The light microscopic appearance of the tumor varies considerably from tumor to tumor, but also within different parts of the same neoplasm. The predominant cell types have a stellate or spindle-shape and they are located within a mucoid extracellular matrix. The tumor has a delicate plexiform capillary network and the neoplastic cells include relatively few lipoblasts that are predominantly univacuolated that contain lipid. The myxoid liposarcoma is an example of a chromosome translocation syndrome in which a translocation [t(12;16)(q13;p11)] between human chromosomes 12 and 16 has been found. It involves the CHOP and FUS genes. The risk of metastatic dissemination relates to the degree of nuclear atypia, hyperchromatism, anaplasia and mitotic activity. The presence of cytoplasmic fat can be identified in frozen tissue sections stained with oil red O and other stains for lipid. The differential diagnosis includes other malignant neoplasms, which may also contain lipid. As a rule liposarcoma is a neoplasm of adults, but rarely it may affect children. A variant of the myxoid liposarcoma is the round cell liposarcoma [liposarcoma - round cell]. When present in the orbit the recommended treatment for a myxoid liposarcoma is a wide resection, but an exenteration may be necessary to prevent recurrence. Regardless of therapy there is a high risk of distant metastases.