When to suspect MPNST

Known NF1 with a plexiform neurofibroma that becomes rapidly larger, harder, more painful or neurologically symptomatic.
New persistent or nocturnal pain in a nerve-sheath lesion, especially if pain is escalating rather than longstanding and stable.
Deep-seated mass, fixation to deeper planes, size over 5 cm, rapid growth or recurrence after excision.
New paraesthesia, weakness, sensory loss or nerve-distribution symptoms.
Prior radiotherapy is a recognised risk context for secondary sarcoma including MPNST.

Pathology and biology

MPNST is a malignant spindle-cell sarcoma showing nerve-sheath differentiation; morphology overlaps with other spindle-cell sarcomas and melanoma.
NF1-associated MPNST usually arises through progression from plexiform neurofibroma through atypical neurofibromatous neoplasm of uncertain biological potential (ANNUBP).
S100 and SOX10 may be positive but are often patchy or reduced compared with benign schwannian lesions.
Loss of H3K27me3 expression supports MPNST in the right context but is not completely sensitive or specific.
Differentials include melanoma, synovial sarcoma, leiomyosarcoma, DFSP with fibrosarcomatous change, desmoid tumour and undifferentiated pleomorphic sarcoma.

Refer suspected cases urgently to a sarcoma MDT before biopsy or excision wherever possible.
MRI is the key local imaging test for defining nerve involvement, deep extension, compartment anatomy and resectability.
Core biopsy should be planned so that the biopsy tract can be managed at definitive surgery.
Staging commonly includes CT chest because lung metastasis is a key concern in high-grade soft-tissue sarcoma.
PET/CT can be useful in NF1 when distinguishing benign plexiform neurofibroma from malignant transformation, according to sarcoma-team practice.

Main curative treatment is planned wide surgical excision aiming for an R0 margin, balanced against function and neurovascular anatomy.
Radiotherapy is commonly considered for high-grade, large, deep or close/positive-margin disease as part of sarcoma MDT planning.
Chemotherapy is not routine for every case but may be considered for selected high-risk, unresectable or metastatic disease.
Unplanned marginal excision can compromise local control and reconstruction options; suspected MPNST should be imaged and biopsied first.
Reconstruction planning should follow oncological clearance and may require plastic surgery, sarcoma surgery and peripheral nerve expertise.

MPNST has substantial local recurrence and metastatic risk; prognosis is worse with large size, deep location, positive margins, high grade and NF1 association in many cohorts.
Follow-up is sarcoma-protocol driven with surveillance of the primary site and chest imaging according to MDT risk stratification.
NF1 patients require education about red flags in existing plexiform lesions and rapid reporting of new pain, growth or neurological symptoms.
Local recurrence should be assessed through the sarcoma MDT rather than treated as a simple recurrent scar nodule.
Because evidence is limited and disease is rare, decisions should be individualised within a specialist sarcoma service.