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Pathology for Urologists

Dedifferentiated Liposarcoma (LPS)


Image A
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Image B
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  • Characterized by the coexistence of well-differentiated and poorly differentiated nonlipogenic areas, either within the same tumor or between a primary tumor and its recurrence/metastasis.
  • Most often encountered in the retroperitoneum.
  • Histology:
    • Transition from well-differentiated LPS to non-lipogenic sarcoma (image A) & (image B).
    • Lipogenic component shows atypical fat with lipoblasts.
    • Non-lipogenic sarcoma appears variable, can be high-grade (e.g. pleomorphic sarcoma, myxofibrosarcoma) or low grade (e.g. fibroblastic) spindle cells.
    • A subset will show heterologous differentiation (rhabdomyosacoma, leiomyosarcoma, osteo- or chondrosarcoma, angiosarcoma).
  • Like well-differentiated LPS shows amplified sequence of Chr 12q14-15.
  • Immunohistochemistry: S100+, MDM2+ and CDK4+; keratin-.
  • Poor prognosis, local recurrence in up to 40% and metastisis in 20% of cases.
  • DDX:
    • Retroperitoneal LPS may extend into the kidney and simulates a primary renal malignancy, particularly:
      • RCC with sarcomatoid change: look for well differentiated (non-transformed) areas of RCC; keratin+, MDM-, CDK4-.
      • Muscle predominant angiomyolipoma: mature fat and with abnormal thick hyalinized vessels; HMB45+.
      • Examine "normal fat" around the tumor/kidney, which may represent well-differentiated LPS of the dedifferentiated LPS.
    • Leiomyosarcoma: spindle cells with cigar-shaped nuclei; actin and desmin+; MDM and CDK4-.

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