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Pathology for Urologists

Rhabdomyosarcoma (RMS)

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  • Malignant tumor that recapitulates features of skeletal muscles.
  • Most common bladder tumor in pediatric patients; very rare in adults.
  • Vast majority are embryonal type; adult RMS are often alveolar type or unclassifiable.
  • More common in males, usually present with hematuria and obstruction.
  • Typically forms polypoid mass (sarcoma botryoides or bunch of grapes) (image A).

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  • Histology:
    • Variable round and spindle cells (image B) & (image C).
    • Should see scattered "strap cells" or "tadpole cells" (rhabdomyoblasts) (image D).
    • In botryoid embryonal subtype, stroma is loose and hypocellular except at the tumor edges where the neoplastic cells condense just beneath the urothelial mucosa (cambium layer).
  • Immunohistochemistry: expresses skeletal muscle markers MyoD1 and myogenin (nuclear positivity).
  • Embryonal RMS in children have excellent prognosis; RMS in adults have poor prognosis.


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