Malignant Peripheral Nerve Sheath Tumor
Bruce M. Wenig, MD
Key Facts
Terminology
Malignant tumor of peripheral nerves or having differentiation along the lines of various elements of nerve sheath
Occurs de novo (sporadic) or in association with NF1
Clinical Issues
Accounts for approximately 5-10% of all soft tissue sarcomas
Up to 20% may occur in head and neck
Approximately 25-50% of all MPNST occur in association with NF1
Most common site of involvement is neck
Less frequently, other sites of involvement include sinonasal tract, nasopharynx, oral cavity
Microscopic Pathology
Cells have elongated nuclei with irregular contour, tapered ends
Nuclei appear wavy or buckled in profile and asymmetrically oval en face
Nuclear palisading may be seen
In sinonasal cavity, MPNST can occur in setting of inflammatory polyp
Divided into low– and high–grade tumors depending on degree of cellularity, pleomorphism, mitotic activity, and necrosis
Ancillary Tests
S100 protein reactivity seen in 50-90% of tumors with extent and intensity of reactivity dependent on histologic grade of tumor
 Low-grade MPNST shows fascicular growth with “wavy” appearing nuclei. As compared to benign schwannomas, there is increased cellularity with nuclear pleomorphism and increased mitotic activity  . |
 In low-grade MPNSTs, S100 protein staining tends to be diffuse and strong, similar to that in benign schwannomas. Differentiation is based on cellularity, atypia, mitotic activity, and infiltrative growth. |
TERMINOLOGY
Abbreviations
Malignant peripheral nerve sheath tumor (MPNST)
Synonyms
Malignant schwannoma
Neurogenic sarcoma
Neurofibrosarcoma
Definitions
Malignant tumor of peripheral nerves or having differentiation along the lines of various elements of nerve sheath
Occurs de novo (sporadic) or in association with neurofibromatosis type 1 (NF1)
ETIOLOGY/PATHOGENESIS
Neurofibromatosis
Occurs in setting of NF1
Idiopathic
De novo (sporadic) MPNST
Post Irradiation
Infrequently may occur in areas previously irradiated
CLINICAL ISSUES
Epidemiology
Incidence
Accounts for approximately 5-10% of all soft tissue sarcomas
Most commonly occurs in lower extremity
Up to 20% may occur in head and neck
Approximately 25-50% of all MPNST occur in association with NF1
Estimated risk of patients with NF1 developing MPNST varies (4-50%)
Occurrence typically follows latent period of 10-20 years
Age
De novo MPNST
Occurs over wide age range, but most frequently in 5th decade
MPNST associated with NF1
Primarily seen in 3rd-4th decades of life
Gender
De novo MPNST
No gender predilection or slightly more common in females
MPNST associated with NF1
No gender predilection or slightly more common in females
Site
Most common site of involvement is neck
Less frequently, other sites of involvement include sinonasal tract, nasopharynx, oral cavity
Presentation
Neck symptoms include
Mass with associated pain, paresthesia, weakness
Sinonasal tract, nasopharynx, oral cavity symptoms include
Mass lesion, pain, epistaxis, and nasal obstruction
Treatment
Surgical approaches
Complete surgical excision is treatment of choice
Most MPNSTs are high-grade malignancies necessitating wide en bloc resection and postoperative radiotherapy
Adjuvant therapy
Chemotherapy utilized for inoperable tumors and disseminated tumors
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