Clinical features
- Less than 3% of soft-tissue sarcomas in children and adolescent
- Primitive mesenchymal cell tumour with signs of early lipogenesis and minor population of mature adipocyte cells
- Myxoid and round cell liposarcoma belong to the same genetic entity
- Round cell liposarcoma – increased potential of recurrence and metastasis
- Young adults, between 10 and 15 years
- Deep lesions
- Frequent in the thigh (60-70%)
- Deep lesions can reach 15 cm
Fig 22 – Myxoid liposarcoma –Myxoid stroma with plexiform capillary network (Giemsa)
- Lipoblasts in various stages of differentiation ( primitive mesenchymal cells to well differentiated lipoblasts)
- Spindle-shaped cells in various proportions
- Small univacuolated cells with irregular and hyperchromatic nuclei
- Hyperchromatic atypical and scalloped nuclei
- Mitotic rate is low
- Uniform, round, small tumour cells with occasional lipid vacuoles (from the small cell component)
- High nuclear to cytoplasmic ratio
- Eccentric hyperchromatic nuclei
- Prominent nucleoli
- Acidophilic cytoplasm
- Fibrillary myxoid background
- Branched delicate capillaries in a myxoid matrix
Histochemical Stains
- Myxoid matrix stains with Alcian blue at pH2.5 and not pH1.0
Immunocytochemistry
- S100 protein: Positive
- CD34: Negative
Genetic Studies
- Ring Chromosome 12
- t(12;16)(q13;p11) – CHOP-TLS/FUS fusion gene
- t(12;22)(q13;p12) – CHOP-EWS fusion gene-(alternative in 10%)
Differential Diagnosis
- Lipoblastoma
- Differential diagnosis can be difficult and sometimes genetic studies are needed
- Extraskeletal myxoid chondrosarcoma
- Absence of delicate capillaries
- Cells do not harbour lipid vacuoles in their cytoplasm
- Alcan blue PH 1.0 staining
- Lymphoma and small round cell tumour
- Immunohistochemical studies are helpful in different differential diagnosis
Main points
- Round cell liposarcoma – hypercellular and less differentiated form of myxoid liposarcoma
- Local recurrence prior to metastasis
- Metastasis to the lung (20-30%)
- Poor prognosis if round or pleomorphic cells are present
- Wide excision is the optimal treatment to avoid local recurrences.