American Urological Association - Renal Sarcomas
- 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.