Home Education AUAUniversity Education Products & Resources Pathology for Urologists Retroperitoneum Leiomyosarcoma


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Image B

  • Account for ~10% of all soft tissue sarcomas.
  • 50% of LMSs occur in retroperitoneum, making it the most common site for this tumor type.
  • Clinical: 2/3 occur in females; median age 60 years.
  • Gross:
    • Gray white masses with hemorrhage and necrosis.
    • Average size 16 cm/ 1600 g.
  • Histology:
    • Elongated/spindle cells with cigar-shaped nuclei and a moderate amount of bright eosinophilic cytoplasm (image A), (image B), & (image C).
    • Perinuclear vacuolization may occur with glycogen accumulation.
    • Mitoses vary, but 80% of retroperitoneal LMSs have > 5 mitotic figures per high-power field.
    • Nuclear atypia.

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Image D

  • Immunohistochemistry: actin+ (image D) and desmin+.
  • Prognosis: Extremely aggressive tumors that cause death by local extension or metastases (lung and liver); 5-year survival is 0-29%.
  • DDX: (Same as in dedifferentiated liposarcoma)
    • Dedifferentiated liposarcoma: has well-differentiated liposarcoma (malignant fat) component; MDM+ and CDK4+.
    • Sarcomatoid RCC: mixed with usual differentiated RCC morphology; keratin+.
    • Muscle predominant angiomyolipoma: abnormal thick hyalinized vessels; melanoma marker HMB-45+.