Breast malignant
OLD Malignant peripheral nerve sheath tumor (MPNST)

Topic Completed: 1 November 2016

Minor changes: 22 June 2020

Copyright: 2002-2019,, Inc.

PubMed Search: Malignant Peripheral Nerve Sheath Tumor [title] breast

Emily S. Reisenbichler, M.D.
Page views in 2020 to date: 21
Cite this page: Reisenbichler ES. OLD MPNST. website. Accessed August 7th, 2020.
Definition / general
  • Spindle cell sarcoma showing histologic, immunohistochemical or ultrastructural features of Schwann cell differentiation
  • Not a part of WHO classification in the breast
Essential features
  • Accounts for less than 10% of all soft tissue sarcomas; exceedingly rare in breast
  • May occur sporadically or arise from a preexisting nerve sheath tumor, usually a neurofibroma in a neurofibromatosis 1 (NF1) patient
  • Shows varied morphology ranging from spindled (fibrosarcoma-like) to epithelioid cytology
  • Rare / patchy staining makes this a difficult tumor to diagnose by immunohistochemistry, particularly in sporadic cases
Clinical features
  • Typically presents as large, palpable mass (mean size > 5 cm)
  • Low grade MPNST: resembles neurofibroma but with increased cellularity and scattered mitotic activity
  • High grade MPNST: resembles a high grade spindle cell sarcoma
  • Epithelioid type
  • Malignant Triton tumor: contains areas of rhabdomyoblastic differentiation
Prognostic factors
  • Association with NF1 portends a worse prognosis
Case reports
  • Like most soft tissue tumors, wide excision with negative margins is the mainstay of treatment
  • Radiation may reduce recurrence but data is limited due to its rarity
Gross description
  • Large tumor with solid cut surface and generally circumscribed borders
Microscopic (histologic) description
  • Typically spindle cell cytology but can be epithelioid
  • Wavy, buckled nuclei
  • Fascicles of alternating hyper- and hypocellular areas
  • Collagenous stroma
  • Perivascular accentuation, often with areas of necrosis
  • Can see areas of heterologous differentiation (osteo-, chondro- or rhabdomyosarcomatous differentiation)
  • Rare cases may show glandular differentiation
Microscopic (histologic) images

Contributed by Dr. Emily S. Reisenbichler

Left: 10x; Right: 20x

Contributed by Dr. Mark R. Wick

Images hosted on other servers:

H&E, S100


Positive stains
  • S100: typically focal / patchy; low grade MPNST arising in a neurofibroma and epithelioid MPNST may be diffusely positive
  • SOX10, GFAP, CD34
  • Desmin: may highlight areas of rhabdomyoblastic differentiation
Negative stains
  • Keratins: except in rare cases with glandular differentiation
  • INI1 loss in a portion of epithelioid variant
Molecular / cytogenetics description
  • Complex karyotypes but no known consistent molecular alterations
Differential diagnosis
  • Dedifferentiated liposarcoma: both liposarcoma and MPNST may show MDM2 overexpression by immunohistochemical staining but dedifferentiated liposarcoma should show genuine MDM2 amplification by FISH; also CDK4 positive
  • Leiomyosarcoma: expression of smooth muscle markers (SMA, desmin, h-Caldesmon)
  • Neurofibroma: less cellular than MPNST and lacking significant nuclear atypia or mitotic activity (in an NF1 patient, virtually any mitotic activity is diagnostic of MPNST)
  • Rhabdomyosarcoma: desmin and muscle specific actin positive with nuclear MyoD1 and myogenin staining; MPNST with rhabdomyoblastic differentiation is usually a focal finding and typical MPNST morphology predominates
  • Spindle cell melanoma: diffuse S100 and SOX10 staining seen in melanoma is unusual in MPNST
  • Synovial sarcoma: monophasic type resembles MPNST morphologically but often shows patchy / focal EMA and keratin staining; biphasic type resembles a glandular MPNST and will show strong keratin staining of the glandular component; both MPNST and synovial sarcoma may show focal S100 or SOX10 staining but synovial sarcoma is characterized by a t(X;18)(p11;q11) translocation
  • Undifferentiated spindle cell sarcoma: by definition is a diagnosis of exclusion showing no specific line of differentiation
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