Soft tissue sarcomas are rare mesenchymal tumours, which originate in
non-epithelial connective tissue sources; liposarcomas are the most
common soft tissue sarcomas.
(2) Five histopathologic subgroups of liposarcomas have been identified, as follows: well differentiated; myxoid; round cell; dedifferentiated; and pleomorphic variants.
Myxoid liposarcoma is the most common subtype of liposarcoma, representing approximately one-third of all liposarcomas.
(3) Myxoid soft-tissue sarcomas encompass a heterogeneous group of rare tumours characterized by a marked abundance of mucoid/myxoid extracellular matrix.
[The main clinicopathological entities in this group are myxoid liposarcoma, low-grade fibromyxoid sarcoma, extraskeletal myxoid chondrosarcoma, myxofibrosarcoma, myxoinflammatory fibroblastic sarcoma, and myxoid dermatofibrosarcoma protuberans.]
(4) The working group of the World Health Organization (WHO) for classification of tumours of soft-tissue and bone combined myxoid and round cell liposarcomas under myxoid liposarcoma.
(5) Liposarcomas may arise in any fat region. Myxoid liposarcoma occurs predominantly in the deep soft-tissues of lower extremities and rarely occur in the retroperitoneum.
(6) The incidence of myxoid liposarcomas is high during the fourth and fifth decades of life, and there is no gender predilection.
(7) Pure myxoid liposarcoma is considered low-grade and has a 5-year survival rate of 90%.
(8) In contrast, myxoid liposarcomas containing a greater than 5% round cell component is considered high-grade and has a worse prognosis.
(9) In contrast to other soft-tissue sarcomas, myxoid liposarcoma tends to metastasize to unusual sites such as retroperitoneum, opposite extremity, and bone.
(10) Histologically, pure myxoid liposarcomas is composed of primitive mesenchymal cells in a myxoid matrix, often featuring mucinous pools.
(11) Lipoblasts are most often univacuolated, small, and tend to cluster around vessels or at the periphery of the lesion.
(12) A delicate plexiform capillary vascular network ('crow's feet' or 'chicken wire pattern' ) is present and provides an important clue for distinguishing myxoid liposarcomas from intramuscular myxoma.
(13) A subset of myxoid liposarcoma shows histological progression to hypercellular or round cell morphology. The round cell areas are characterized by solid sheets of primitive round cells with a high nuclear/cytoplasmic ratio and a prominent nucleolus.
(14) Myxoid liposarcoma is characterized by a recurrent translocation t(12;16)(q13;p11) in more than 90% of cases.
(15) Most cases of myxoid liposarcomas are one of three different FUS-DDIT3 fusion transcript types, including varying portions of FUS. The FUS-DDIT3 fusion transcript type does not appear to have a significant impact on clinical outcome.
(16) Myxoid liposarcoma with a type 1 EWSR1-DDIT3 fusion transcript may show more favorable clinical behavior than those with other types of fusion transcripts.
(17) Several receptor tyrosine kinases (RTKs) are highly expressed in myxoid liposarcoma , including RET, MET, and IGF1R.
(18) Purely myxoid lesions are characterized by a 5-year survival rate of approximately 70%, which drops to approximately 20% in the case of round cell tumours.
(19) Patients who present with multifocal disease have a poor prognosis and the presence of necrosis and p53 overexpression have been found to be independent predictors of poor prognosis.
Local recurrence has been reported with an unusually high incidence of soft tissue and bone metastases to the lung.
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