Embryonal Rhabdomyosarcoma



Embryonal Rhabdomyosarcoma


Khin Thway, BSc, MBBS, FRCPath









Embryonal rhabdomyosarcoma of the bladder is seen under urothelium image. It is mostly of low cellularity and not easily identifiable at low power when the appearances can be mistaken for inflammation.






The tumor cells show a range of appearances. There are relatively undifferentiated ovoid cells image along with rhabdomyoblasts with prominent eosinophilic cytoplasm and eccentric nuclei image.


TERMINOLOGY


Abbreviations



  • Embryonal rhabdomyosarcoma (ERMS)


Definitions



  • Malignant soft tissue tumor that shows variable differentiation toward embryonic skeletal muscle


  • ERMS encompasses botryoid, spindle cell, and anaplastic variants


ETIOLOGY/PATHOGENESIS


Unknown



  • Cell of origin still unknown



    • Possible candidate cells include muscle stem cells and multipotent mesenchymal stem cells


  • Often occur in sites lacking skeletal muscle



    • e.g., bladder, prostate


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Rhabdomyosarcomas (RMS) are most frequent soft tissue sarcomas in children and young adults


    • ERMS is most common RMS subtype



      • 4.3 cases per 1,000,000 children/year in USA


      • Represent 60-70% of RMS


  • Age



    • Children


    • ERMS generally affects younger population than alveolar RMS


    • Typically < 10 years of age



      • Majority in children < 5 years


      • Bimodal distribution with smaller peak in adolescence


      • Occasional cases congenital


    • Rarer in adults



      • Where pleomorphic subtype predominates


  • Gender



    • Slight male preponderance


    • M:F= 1.4:1


Site



  • Head and neck



    • Particularly orbital and parameningeal sites


  • Genitourinary region



    • Bladder


    • Prostate


    • Paratesticular soft tissue


  • Other sites



    • Retroperitoneum and pelvis


    • Biliary tract


  • Much less frequent involvement of trunk and limbs than alveolar rhabdomyosarcoma (ARMS)


  • Spindle cell RMS



    • Paratesticular region


  • Botryoid RMS



    • Arise beneath mucosal epithelial surfaces



      • Bladder


      • Vagina


      • Extrahepatic bile ducts


      • More rarely, auditory canal or conjunctiva


Presentation



  • Suddenly enlarging mass



    • Local symptoms pertaining to site of origin



      • e.g., deafness, proptosis (head and neck)


      • e.g., urinary retention (genitourinary sites)


Prognosis



  • Main prognostic parameters are histologic type, disease stage, and site


  • Favorable sites are head and neck (nonparameningeal), genitourinary (nonbladder, nonprostate), and bile duct


  • Botryoid and spindle cell variants (excluding aggressive adult spindle cell variant) have better prognosis




  • ERMS has significantly better prognosis than ARMS


  • 5-year overall survival approximately 73%


MACROSCOPIC FEATURES


General Features



  • Fleshy mass


  • Margins usually infiltrative


  • Tan to white


  • Rubbery cut surface


  • Hemorrhage


  • Necrosis


  • Cystic degeneration


  • Botryoid RMS



    • Exophytic, polypoid tumor


    • More circumscribed margins


    • Small nodules adjacent to mucosal surface


    • Masses may fill lumen of hollow viscus


    • Gelatinous cut surface


MICROSCOPIC PATHOLOGY


Histologic Features

Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Embryonal Rhabdomyosarcoma
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