Diagnosis generally reserved for any spindle cell sarcoma arising from a nerve or neurofibroma, or showing nerve sheath differentiation.
At least half of MPNST's occur in patients with neurofibromatosis (although only 4-5% of NF-1 patients experience malignant transformation of their tumors).
Cytogenetic may shows complex structural and numerical chromosomal alteration and frequent loss of NF1 and p53.
Adults: 20's to 50's; men > women.
Usually associated with large nerve trunk so most common in the proximal portions of upper and lower extremities and trunk.
Gross: fusiform or eccentric swellings within a major nerve; may have secondary areas of hemorrhage or necrosis (image A).
Majority are spindle cells (80%).
Nuclei are wavy or "comma-shaped."
Presence of mitotic activity within a neurofibroma is helpful criterion used in establishing a diagnosis of malignancy.
Other features supportive of malignancy: greater cellularity and nuclear pleomorphism (image B).
Less often may have epithelioid morphology.
A subset (15%) may show heterologous differentiation such as osteo- or chondrosarcoma, rhabdomyosarcoma, angiosaroma.
Immunohistochemistry: S-100 (+) (usually focal and not strong diffuse positivity seen in schwannoma).
Prognosis: Aggressive tumors with 5 year survival rate of 15-34%; high recurrence rate (>40%) and metastasis (up to 60%) commonly to the lung (mostly) and bone.