Updates in Peripheral Nerve Sheath and Adipocytic Tumors

Certain areas in peripheral nerve sheath and adipocytic neoplasm diagnosis historically were characterized by a lack of clarity and consensus regarding terminology, diagnostic criteria, and prognosis. Recent work has led to important clarifications in diagnostic criteria and/or outcome data for neurofibromas with atypia and MDM2 amplification-negative adipocytic tumors. However, these clarifications remain incompletely recognized by many pathologists, in part due to the paucity of these neoplasms. This paper reviews the history and recent advances in diagnostic criteria, terminology, and understanding of prognosis for neurofibromas with atypia, malignant peripheral nerve sheath tumor (MPNST), malignant melanotic nerve sheath tumor, and atypical spindle cell/pleomorphic lipomatous tumor. Melanoma may be histologically identical to MPNST, and this paper also provides an overview of helpful clinical and molecular features that allow accurate identification of melanoma, including undifferentiated, dedifferentiated, and transdifferentiated melanoma, and their distinction from MPNST.