Low-Grade Myofibroblastic Sarcoma



Low-Grade Myofibroblastic Sarcoma


Thomas Mentzel, MD









Low-grade myofibroblastic sarcoma is characterized by a diffuse infiltration of preexisting structures, as in this case, in which a diffuse infiltration of preexisting skeletal muscle is seen.






Low-grade myofibroblastic sarcoma composed of spindled cells shows myofibroblastic features. Tumor cells contain an ill-defined, pale eosinophilic cytoplasm and fusiform, slightly atypical nuclei.


TERMINOLOGY


Abbreviations



  • Low-grade myofibroblastic sarcoma (LGMFS)


Synonyms



  • Myofibrosarcoma


Definitions



  • Distinct atypical myofibroblastic neoplasm with fibromatosis-like morphologic features


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Rare low-grade sarcoma


  • Age



    • Occurs predominantly in adult patients


    • Children are rarely affected


  • Gender



    • Slight male predominance


Site



  • Wide anatomic distribution


  • Occurs frequently in head and neck region



    • Tongue and oral cavity are preferred locations


  • Occurs frequently in extremities


  • Subcutaneous and deep soft tissue


  • Very rare in dermal location


Presentation



  • Deep mass


  • Painless mass


Treatment



  • Surgical approaches



    • Complete excision


Prognosis



  • Locally aggressive behavior


  • Increased rate of local recurrences


  • Often repeated local recurrences


  • Metastases occur only rarely and often after prolonged time interval


IMAGE FINDINGS


Radiographic Findings



  • Destructive growth pattern


MACROSCOPIC FEATURES


General Features



  • Firm tumor mass


  • Infiltrative, ill-defined neoplasms


  • Pale gray-white, fibrous cut surfaces


Size



  • May reach considerable size


MICROSCOPIC PATHOLOGY


Histologic Features



  • Diffusely infiltrative growth


  • Tumor cells may grow diffusely between individual preexisting cells and structures


  • Cellular spindle cell fascicles


  • May show storiform growth


  • Hypocellular neoplasms are rare


  • Collagenous stroma


  • Focal stromal hyalinizations may be seen


  • Stroma may contain increased number of thin-walled capillaries


  • Low to moderate degree of cytologic atypia


  • Mitoses may be seen


  • Usually no tumor necrosis


  • May progress to higher grade malignant neoplasm



Cytologic Features



  • Spindle-shaped tumor cells


  • Ill-defined, pale eosinophilic cytoplasm


  • Fusiform nuclei


  • Nuclei are elongated with evenly distributed chromatin


  • Nuclei are vesicular with indentations and small nucleoli


  • Moderate nuclear atypia with enlarged, hyperchromatic, and irregular nuclei


ANCILLARY TESTS


Electron Microscopy



  • Tumor cells show myofibroblastic features



    • Indented, clefted nuclei


    • Variable amount of rough endoplasmic reticulum


    • Subplasmalemmal myofilaments (stress fibers) with focal densities


    • Paucity of subplasmalemmal attachment plaques


    • Absent basal lamina and pinocytotic vesicles


  • Abundant extracellular collagen


DIFFERENTIAL DIAGNOSIS


Desmoid Fibromatosis



  • Infiltrative growth but no diffuse “growing through preexisting structures”


  • No cytologic atypia


  • Perivascular edema


  • β-catenin(+)


  • Desmin usually negative


  • Focal and weak expression of actins


Leiomyosarcoma



  • Often pushing margins


  • Spindled tumor cells with deep eosinophilic, fibrillary cytoplasm


  • Spindled, cigar-shaped nuclei


  • Paranuclear vacuoles


  • HCAD(+)


Fibrosarcoma



  • Extremely rare


  • Herringbone growth pattern


  • Small rim of cytoplasm and enlarged spindled nuclei


  • No expression of myogenic immunohistochemical markers


Spindle Cell Rhabdomyosarcoma



  • Very rare


  • Scattered rhabdomyoblasts


  • Focal nuclear expression of myogenin

Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Low-Grade Myofibroblastic Sarcoma
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