Malignant Peripheral Nerve Sheath Tumors Masking as Ewing Sarcoma/Primitive Neuroectodermal Tumors.

Malignant peripheral nerve tumors, a small subset of soft tissue sarcomas, provide a unique diagnostic challenge. Although they may arise from peripheral nerves or from cells associated with nerve sheaths, malignant peripheral nerve tumors often present with diverse immunohistochemical features similar to those of other tumors. These features make MPNSTs difficult to diagnose and classify. We present a case of a 26-year-old female presenting with a rapidly growing soft tissue mass. The mass was excised and immunohistological staining suggested a Ewing's sarcoma/Primitive neuroectodermal tumor. Confirmational studies did not confirm this diagnosis and upon further review, the diagnosis was changed to a malignant peripheral nerve sheath tumor. We reviewed this case in the setting of the reported literature concerning MPNSTs with focus on the epidemiologic, diagnostic, and immunohistologic features that distinguish this tumor from other similar malignancies.