Consistent with the diagnosis of high-grade MPNST, the majority of NF1 and sporadic MPNST had high cellularity, conventional histology, high mitotic rate, and presence of necrosis; p53 staining was positive in most tumors, and the proliferation index (MIB-1) was high in most tumors (for details, see Supplementary Appendix Table S4). This evidence concerns the gene TP53 and malignant peripheral nerve sheath tumor.