Myxoid/round cell liposarcoma

Myxoid/round cell liposarcoma (MRCLS), also known as myxoid liposarcoma, is a malignant soft tissue tumor that arises from fat cells (adipocytes). It is one of the most common subtypes of liposarcoma, a group of cancers that develop in fatty tissue. MRCLS is characterized by a specific chromosomal translocation, most commonly t(12;16)(q13;p11), which results in the FUS-DDIT3 (also called TLS-CHOP) fusion gene. Less frequently, a t(12;22)(q13;q12) translocation producing an EWSR1-DDIT3 fusion gene is identified. This genetic alteration is considered the hallmark of the disease and is used for diagnostic confirmation. The tumor is not inherited but arises from somatic (acquired) mutations. MRCLS most commonly presents as a painless, slowly growing deep soft tissue mass, typically in the extremities, with a strong predilection for the thigh and popliteal fossa. Unlike other soft tissue sarcomas, MRCLS has a distinctive tendency to metastasize to unusual sites, including the retroperitoneum, opposite extremity, bone, and other soft tissue locations, rather than primarily to the lungs. The round cell component represents the high-grade end of the spectrum; tumors with a higher percentage of round cells (generally greater than 5%) are associated with a worse prognosis, higher rates of metastasis, and decreased overall survival. Treatment of myxoid/round cell liposarcoma typically involves wide surgical excision as the primary approach. MRCLS is notably more sensitive to radiation therapy compared to other soft tissue sarcoma subtypes, and neoadjuvant (pre-operative) or adjuvant radiation is frequently employed. Chemotherapy, particularly regimens containing doxorubicin and ifosfamide, may be used for advanced or metastatic disease. Trabectedin has shown particular efficacy in MRCLS and is used in the treatment of advanced cases. Ongoing research is exploring targeted therapies based on the molecular characteristics of the tumor. Regular long-term surveillance is essential due to the risk of late recurrences and the unusual metastatic patterns associated with this disease.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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