Malignant peripheral nerve sheath tumors (MPNSTs) are sarcomas on peripheral nerves or nerve sheath. These MPNSTs can occur on any cell type and differs from one to other. A sarcoma is regarded as MPNST only when it is raised on the peripheral nerve or it exists on neurofibroma. MPNSTs usually present as an enlarging palpable mass. Pain is a variable complaint
Rapid enlargement occurs more often in the setting of NF1 and should raise concern for malignant degeneration of a neurofibroma. The recurrence rate is reported to be up to 40%, and approximately two thirds metastasize (lungs and bone). Five-year survival is reported to be 26% to 60%, and 10-year survival about 45%.