Superficial Malignant Peripheral Nerve Sheath Tumor



Superficial Malignant Peripheral Nerve Sheath Tumor


David R. Lucas, MD










MPNST can rarely present as a primary skin tumor, such as this scalp tumor excised from a 90-year-old woman. Superficial MPNST typically occurs in mid-to-deep dermis or as a subcutaneous primary.






Unless one sees continuity with a cutaneous nerve or adjacent neurofibroma, immunohistochemistry is required for diagnosis. Often negative or patchy, diffuse S100 staining is present in this case.


TERMINOLOGY


Abbreviations



  • Malignant peripheral nerve sheath tumor (MPNST)


Synonyms



  • Neurofibrosarcoma, “malignant schwannoma” (older terms)


Definitions



  • Superficial sarcoma arising from cutaneous nerve or benign nerve sheath tumor, or showing nerve sheath differentiation



    • Diagnostic criteria



      • Arises from nerve or benign nerve sheath tumor


      • Or shows histological evidence of nerve sheath differentiation in a NF1 patient


      • Or shows histological plus immunohistochemical or ultrastructural evidence of nerve sheath differentiation in non-NF1 patient


ETIOLOGY/PATHOGENESIS


Genetic Predisposition



  • 40% associated with neurofibromatosis type 1 (NF1)



    • Lifetime incidence: 2-16%


Molecular Pathogenesis



  • NF1 caused by germline mutation of NF1 tumor suppressor gene



    • Somatic loss of 2nd NF1 allele required for tumorigenesis


  • Malignant transformation in both NF1-associated and sporadic MPNST often involves INK4A and P53 and their downstream pathways


CLINICAL ISSUES


Epidemiology



  • Incidence



    • MPNST accounts for 5-10% of soft tissue sarcomas



      • Superficial MPNST very rare


  • Age



    • Mostly adults (20-50 years)



      • Average: 40 years


      • Wide range: 4-79 years


  • Gender



    • Women and men roughly equal


Site



  • Head and neck (60%), trunk, upper and lower extremities


  • Dermis &/or subcutis



    • Mid- or deep dermis in most cases


    • May invade deeper structures


Presentation



  • Painful or painless mass


Treatment



  • Surgical approaches



    • Wide excision/resection


  • Adjuvant therapy



    • Radiation


  • Drugs



    • Generally MPNST shows poor response to chemotherapy


Prognosis



  • Local recurrence: 60%


  • Metastasis: 25%



    • Lung, lymph node, bone


  • 30% die of disease



    • Average survival: 3.3 years



IMAGE FINDINGS


General Features



  • Morphology



    • Cutaneous nodule


    • Superficial soft tissue mass


MACROSCOPIC FEATURES


General Features



  • Epidermal alterations absent


  • Coexisting neurofibroma in some cases


Size



  • Average: 3 cm (range: 2-16 cm)


MICROSCOPIC PATHOLOGY


Histologic Features



  • Wide spectrum of cytoarchitectural patterns



    • Mostly intermediate or high-grade sarcomas



      • High mitotic rate and necrosis


      • Only around 15% are low grade


    • Nerve sheath differentiation



      • Nuclear palisading uncommon, usually focal


      • Tactoid differentiation with whorling or Wagner-Meissner body-like features


    • Intraneural tumors



      • Plexiform architecture


      • Microscopic extension within nerve fascicle


    • Tumors arising from preexisting benign nerve sheath tumor



      • Neurofibroma most common, transitional areas, usually in NF1 patients


    • Diffuse infiltrative sarcomatous proliferation without evidence of nerve or nerve sheath tumor origin


  • Spindle cell MPNST (most common pattern)



    • Long fascicles of uniform, closely spaced, hyperchromatic spindle cells


    • Alternating cellular fascicles and hypocellular areas (“tapestry” or “marbled” pattern)


    • Myxoid matrix, focal


    • Storiform arrays


    • Wavy nuclei with tapered ends


    • Small round blue cells


    • Pleomorphic cells



      • Multinucleated giant cells


    • Extensive necrosis with perivascular preservation


  • Epithelioid MPNST



    • Multinodular architecture


    • Cords and clusters in some


    • Large epithelioid cells



      • Abundant eosinophilic cytoplasm


      • Large vesicular nuclei with macronucleoli


      • Clear cytoplasm in some


    • Often mixed with spindle cells


  • Heterologous differentiation (15% of MPNSTs)



    • Osseous and osteosarcomatous


    • Chondroid and chondrosarcomatous


    • Rhabdomyosarcomatous (Triton tumor)


    • Angiosarcomatous


    • Glandular


Cytologic Features



  • Spindle cells



    • Ill-defined cytoplasm


    • Hyperchromatic nucleus with dispersed coarse chromatin


    • Tapered and wavy nuclei in well-differentiated tumors


    • Very brisk mitotic activity in high-grade tumors


  • Epithelioid cells



    • Abundant eosinophilic or clear cytoplasm


    • Vesicular nucleus with prominent inclusion-like nucleolus



ANCILLARY TESTS


Immunohistochemistry



  • S100 protein (+) in about 60% of cases (more often in well-differentiated and epithelioid MPNST), usually focal

Jul 8, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Superficial Malignant Peripheral Nerve Sheath Tumor
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