American Urological Association - Renal Sarcomas
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Renal Sarcomas

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  • Most renal sarcomas are secondary involvement from a retroperitoneal origin.
  • Renal sarcomas arising primarily within the kidney are very rare.
  • Morphologic features are similar to their soft tissue counterparts.
  • Most common is leiomyosarcoma, which may arise from the renal veins and its branches
    (image A) & (image B).
  • Synovial sarcoma is a biphasic tumor composed mostly of mesenchymal spindle cells and focal epithelial cells; exhibits a specific chromosomal translocation t(X;18) and shows SYT-SSX2 gene fusion (soft tissue SS has SYT-SSX1 fusion).
  • Primitive neuroectodermal tumor (PNET) shows primitive round blue cells that are CD99+ and is characterized by t(11;22), which results in fusion of EWSR1 and FLI1 oncogene.
  • Angiosarcoma is exceedingly rare.
  • Liposarcoma may look like fat predominant angiomyolipoma and generally is a secondary extension from the retroperitoneum.
  • Main DDX for sarcoma with spindle cells:
    • Sarcomatoid RCC: Can be mixed with usual RCC morphology and is keratin+ (since it's an epithelial tumor); search for the usual epithelial RCC component to establish the diagnosis.