MALIGNANT PERIPHERAL NERVE SHEATH TUMOR (NEUROFIBROSARCOMA)
Malignant peripheral nerve sheath tumor (MPNST) is a sarcoma that originates from a peripheral nerve, or from nerve sheath cells such as Schwann cells or fibroblasts. The term MPNST has replaced previously used terms such as malignant schwannoma, neurofibrosarcoma, and neurogenic sarcoma.
Of all soft tissue sarcomas, MPNST's comprise approximately 5-10%. They can occur spontaneously, but up to 50% of MPNST's occur in patients with Neurofibromatosis I (von Recklinghausen disease). Patients with NF1 have a 10% lifetime risk of ultimately developing a MPNST, likely arising from a preexisting neurofibroma.
MPNST's are represented by dense cellular fascicles, alternating with myxoid regions. Cells may be rounded or fusiform in shape. Malignancy is suggested by high mitotic activity, nuclear pleomorphism, and invasion of surrounding tissue and vascular structures.
Often present with an enlarging palpable mass. MPNST's are typically deep -seated, and involve the proximal upper and lower extremities and the trunk. Pain is variable. Because the MPNST often arises from large peripheral nerves (sciatic nerve, brachial plexus, sacral plexus) radicular pain, paresthesias, and motor weakness may be presenting complaints.
MRI is the imaging method of choice to visualize MPNST. They can appear similar to their benign counterpart (neurofibroma), but size (> 5 cm), invasion of fat planes, ill-defined margins, surrounding edema, and heterogeneity all suggest a more malignant process.
As with many sarcomas, metastasis is most likely to the lungs, so a CT scan of the chest is also an important part of early workup.
Surgical resection with wide margins is the mainstay of treatment. This method offers the lowest probability of both local recurrence and distant metastases.
Radiation therapy can be used preoperatively to reduce tumor size and make limb salvage technically easier. This does, however, delay surgery, increases chances for wound healing complications, and decreases the amount of tissue for diagnosis. Post operative radiation can also be administered, which allows for larger specimen for diagnosis. Delaying radiation until the postoperative setting, however, may make limb salvage more challenging due to the larger size of the tumor at the time of resection.
Chemotherapy is typically reserved for systemic disease that is too diffuse for local treatment techniques.
Recurrence rates have been reported to range from 40-65% for local recurrence, and 40-68% for distant metastasis. 5-year survival is reported to range from 16-52%. The variability in these numbers is largely correlated with tumor size, completeness of excision, and presence of a low grade component. With improved imaging that has led to earlier diagnosis and aggressive treatment, survival rates have improved and recurrence rates have dropped.
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