myxoid/round cell liposarcoma
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Myxoid and round cell liposarcoma accounts for about 30% to 35% of all liposarcomas and, even if still classified by the World Health Organization (WHO) as 2 distinct subtypes, share both clinical and morphologic features.
Lesions combining both patterns are frequent and wide agreement exists in considering round cell liposarcoma as the high grade counterpart of myxoid liposarcoma.
The clinical course of myxoid/round cell liposarcoma (MRCL) is characterized by frequent local recurrences and metastases at unusual sites. MRCLs carry specific translocations, t(12;16) or rarely t(12;22), linking the FUS or the EWSR1 gene with the DDIT3 gene, respectively.
Synopsis
limbs predominant localization
peak incidence between the third and the fifth decade
overall metastatic rate of approximately 30% (peculiar tendency to metastasize to the soft tissue)
purely myxoid liposarcoma
- hypocellular spindle cell proliferation
- myxoid background
- varying number of monovacuolated lipoblasts
- thin-walled capillary network organized in a plexiform pattern
- hypercellular areas that may exhibits an undifferentiated round cell morphology
myxoid/round cell liposarcoma
- more than 25% hypercellular/round cell areas
round cell liposarcoma
- more than 75% hypercellular/round cell areas
Differential diagnosis
benign tumors
- myxoid spindle cell lipoma
- intramuscular myxoma
- lipoblastoma
malignant tumors
- low grade myxofibrosarcoma
- extraskeletal myxoid chondrosarcoma
Variants
myxoid liposarcoma
round cell liposarcoma
Cytogenetics
t(12;16)(q13;p11) creating DDIT3/FUS fusion gene (12q13 and 16p11) (or CHOP/TLS fusion gene)
t(12;22)(q13;q12) (12q13 and 22q12) creating DDIT3/EWSR1 fusion gene
Molecular biology
CHOP/FUS fusion gene (CHOP at 12q13 and FUS at 16p11)
DDIT3/EWSR1 fusion gene (DDIT3 at 12q13 and EWSR1 at 22q12)
References
Bode-Lesniewska B, Frigerio S, Exner U, Abdou MT, Moch H, Zimmermann DR. Relevance of translocation type in myxoid liposarcoma and identification of a novel EWSR1-DDIT3 fusion. Genes Chromosomes Cancer. 2007 Jul 23; PMID: #17647282#
Orvieto E, Furlanetto A, Laurino L, Del Tos AP. Myxoid and round cell liposarcoma: a spectrum of myxoid adipocytic neoplasia. Semin Diagn Pathol. 2001 Nov;18(4):267-73. PMID: #11757867#