Definition:

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Malignant peripheral nerve sheath tumor arising from a peripheral nerve, neurofibroma or in a patient with neurofibromatosis type 1 (NF1).
If none of these criteria apply, then the diagnosis is relied on a combination of histology and immunophenotyping that reveal a differentiation from Schwann cells.

General:

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Rare tumor (5% of soft tissue tumors)
50% associated with NF1, while 50% arise de novo.
Patients are from 20-50 years, but may arise in children with NF1.
Highly malignant and very aggressive
The sciatic nerve is the most commonly involved nerve.

Radiology:

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No distinct radiological sign, besides from that the tumor has its origo in a peripheral nerve.

Macroscopic description:

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Gross, spindled mass that involves a big nerve. Often bigger than 5 cm, and the cut surface is whitish with bleedings and necrosis.

Histologic description:

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Spindle cells growing in fasciculations and ‘back-to-back’.
Mixture of cellularly dense and less dense areas
Geographic necrosis common
Cells have hyperchromatic nuclei and pale cytoplasm.
May have bizarre cells
Frequent mitotic figures (>4 mitoses/ 10 HPF)

Histologic images:

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source

Positive stains:

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S-100 (<50%), GFAP (20-30%)

Negative stains:

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SMA, Desmin

Molecular analysis and cytogenetics:

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Usually not used in diagnostics, but MPNST is overrepresented in NF1 patients.

Differential diagnosis:

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Fibrosarcoma, monophasic synovial sarcoma, leiomyosarcoma, desmoplastic melanoma, neurofibroma with atypical features

Treatment and prognosis:

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Radical surgery, often follow by radiation therapy.
Poor prognosis (5 year survival rate of about 35%)
Negative predictors: Localisation on truncus, tumor size > 5 cm, high grade tumor and radiation indused tumors.
Recurrence risk 40-65%
Metastasize to lung, bone, pleura, soft tissue, liver and brain
Almost everyone with metastatic disease dies

References:

WHO Classification of Tumours of Soft Tissue and Bone (IARC WHO Classification of Tumours), 4th Edition, 2013, edited by Christopher D. M. Fletcher, Julia A. Bridge, Pancras C. W. Hogendoorn and Fredrik Mertens
Enzinger & Weiss’s Soft Tissue Tumours, 6th Edition, edited by John R. Goldblum, Andrew L. Folpe and Sharon W. Weiss

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