First, the investigators plan to use a retrospective analysis to determine the clinical landscape of neurofibromatosis (NF)1-associated malignant peripheral nerve sheath tumor (MPNST) and precursor lesions (e.g., atypical or nodular plexiform neurofibromas). A worldwide database will be established, collecting, in a standardized manner, histologic, immunohistochemical, molecular, radiographic, treatment, and related clinical data from centers worldwide with expertise in these NF1-related cancers. Although retrospective in nature, the resulting data from this registry may reveal previously unanticipated patterns, similar to the INFACT effort outcome. This registry would then allow the acquisition of data associated with MPNST biospecimens collected under associated banks (frozen or paraffin-embedded, germline (or normal tissue DNA) samples, and any previously somatic whole-exome or whole-genome sequencing data for aggregate analyses). Second, the investigators plan to co-register patients to institutional banks in order to prospectively collect MPNST samples for analysis. These patients will be consented in order to collect the above information and for banking of tumor tissue and future studies that include genomic characterization of the tumors.