Malignant peripheral nerve sheath tumors (MPNSTs), formerly known as neurofibrosarcomas, are tumors that grow around peripheral nerves. They account for less than 10% of peripheral nerve tumors. Patients present with a painful mass along a nerve distribution. Sensory and motor deficits of the nerve are common. MPNSTs tend to occur on the extremities and trunk and along major nerve trunks such as the brachial plexus.

Neurofibromas may transform into MPNSTs. This is of specific concern in patients with neurofibromatosis, who may have a high number of peripheral nerve tumors.

MPNSTs have a poor prognosis generally, with a worse prognosis in people with large tumors or neurofibromatosis. The primary treatment is surgical resection.