Myxoid liposarcoma

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)
Fig 23 - Myxoid liposarcoma –Numerous vacuolated cells. Cells have round to ovoid nuclei (Giemsa)
Fig 24a -  Myxoid liposarcoma –Numerous uni or multivacuolated lipoblasts with eccentric compressed nuclei (H&E)
Fig 24b - Myxoid liposarcoma –Numerous uni or multivacuolated lipoblasts with eccentric compressed nuclei (H&E)
Fig 25 - Myxoid liposarcoma – Malignant lipoblasts with pleomorphic scalloped irregular nuclei (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.
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