Spindle Cell Rhabdomyosarcoma



Spindle Cell Rhabdomyosarcoma


Khin Thway, BSc, MBBS, FRCPath









Low-power view of adult-type spindle cell rhabdomyosarcoma, in which laryngeal squamous epithelium overlies cellular tumor, shows sheets of mildly atypical cells within collagenous stroma.






Juvenile-type spindle cell rhabdomyosarcoma shows sweeping fascicles of spindled cells present in a collagenous matrix. Focal rhabdomyoblastic differentiation is evident image, even at low power.


TERMINOLOGY


Abbreviations



  • Spindle cell rhabdomyosarcoma (RMS)


Definitions



  • Uncommon subtype of rhabdomyosarcoma occurring in both children and adults; composed of largely cellular proliferation of predominantly spindled cells


  • Spindle cell RMS in children is considered variant of embryonal RMS



    • Carries good prognosis compared to other RMS subtypes


  • Adult-type spindle cell rhabdomyosarcoma is aggressive neoplasm


CLINICAL ISSUES


Epidemiology



  • Age



    • Children



      • < 10 years


    • Adults



      • All adult age groups (2nd-8th decades)


      • Median: Approximately 4th-5th decades


  • Gender



    • Male preponderance


Site



  • Children



    • Most tumors occur in paratesticular region


  • Adults



    • Most common in head and neck region



      • > 50% of cases


    • Retroperitoneum


    • Extremities


    • Trunk


    • Vulva


    • Paratesticular region


  • Tumors usually deeply located


Presentation



  • Suddenly enlarging mass



    • Local symptoms pertaining to site of origin


Prognosis



  • Behavior varies significantly between children and adults, suggesting distinct clinicopathologic subtypes



    • Good prognosis in children (when compared to other RMS subtypes)


    • Clinically aggressive in adults



      • Lymph node or blood-borne metastases


MACROSCOPIC FEATURES


General Features



  • Firm white mass


Size



  • Variable: 1-30 cm



    • Mean: 8 cm


MICROSCOPIC PATHOLOGY


Histologic Features



  • Juvenile type



    • Fascicular architecture



      • Sweeping or loose fascicles


      • Some tumors have storiform pattern


    • Usually hypercellular


    • Spindle cells



      • Elongated nuclei


      • Nuclei can be vesicular or hyperchromatic


      • Nucleoli may be prominent


      • Pale or amphophilic fibrillary cytoplasm


      • Cross-striations


      • Prominent cell borders


    • Rhabdomyoblasts




      • Variable numbers


      • Spindle or polygonal


    • Variable amounts of intervening collagen



      • Collagen-rich type shows abundant collagen fibers, with cells in short fascicles or storiform arrangements


      • Collagen-poor type is more cellular


    • Mitotic figures usually prominent


    • Frankly pleomorphic areas absent


    • No round cell foci


  • Adult type



    • Long or intersecting fascicles


    • Atypical spindle cells



      • Elongated, vesicular nuclei


      • Pale or amphophilic fibrillary cytoplasm


    • Scattered spindle or polygonal rhabdomyoblasts



      • Usually present in small numbers


      • Abundant eosinophilic cytoplasm


    • Prominent mitoses with atypical forms


    • Necrosis in some tumors



      • Sclerosing pseudovascular features in a smaller number


    • No round cell or pleomorphic areas


ANCILLARY TESTS


Immunohistochemistry



  • Desmin(+)



    • Characteristically strong and diffuse cytoplasmic expression


  • Myogenin(+) and MYOD1(+)



    • Myogenic nuclear regulatory proteins


    • Nuclear expression is specific for RMS



      • May be scanty or focal


    • Any cytoplasmic staining should be disregarded


  • HHF-35 (muscle specific actin)(+)


  • SMA frequently positive


  • Occasional cases cytokeratin and epithelial membrane antigen positive


  • H-caldesmon(-)


  • S100 protein(-)


DIFFERENTIAL DIAGNOSIS


Rhabdomyoma



  • Predilection for head and neck



    • Especially fetal type


  • Fetal rhabdomyoma



    • No atypia or necrosis


    • Mitoses usually absent


  • Adult rhabdomyoma



    • Male preponderance


    • Circumscribed lesion


    • Large polygonal cells, abundant cytoplasm


  • Genital rhabdomyoma



    • Mostly middle-aged women


    • Mostly vagina; also vulva and cervix


Desmoid Fibromatosis



  • Long fascicles of spindle and stellate myofibroblasts


  • Vesicular nuclei


  • Small pinpoint nucleoli


  • Fibrillary cytoplasm


  • No cytologic atypia


  • Distinct vascular pattern



    • Small thick-walled and larger thin-walled vessels


  • Prominent collagenous stroma


  • Nuclear β-catenin expression


  • Desmin usually negative


  • Focal and weak expression of actins


  • β-catenin or APC mutations


Nodular Fasciitis

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