This indicates that in the context of NF1-associated tumors, the Nf1+/− microenvironment has the capacity to accelerate the formation of benign lesions (pNF) but restrain the further progression to frank sarcoma (MPNST), as observed with models of non-NF1-associated papilloma and SCC (i.e. DMBA/TPA-induced skin tumors). This evidence concerns the gene NF1 and malignant peripheral nerve sheath tumor.