Purpose: Neurofibromatosis type1 (NF1) is an autosomal dominant condition that predisposes to benign and malignant tumors. The lifetime risk of a malignant peripheral nerve sheath tumor (MPNST) in NF1is f10%.These tumors have a poor survival rate and their molecular basis remains unclear.We report the first comprehensive investigation of DNA copy number across multitude of genes in NF1tumors using high-resolution array comparative genomic hybridization (CGH), with the aim to identify molecular signatures that delineate malignant from benign NF1tumors. Experimental Design: We constructed an exon-level resolution microarray encompassing 57 selected genes and profiled DNA from 35 MPNSTs, 16 plexiform, and 8 dermal neurofibromas. Bioinformatic analysis was done on array CGH data to identify concurrent aberrations in malignant tumors. Results: The array CGH profiles of MPNSTs and neurofibromas were markedly different. A number of MPNST-specific alterations were identified, including amplifications of ITGB4, PDGFRA, MET, TP73, and HGF plus deletions in NF1, HMMR/RHAMM, MMP13, L1CAM2, p16INK4A/ CDKN2A, andTP53. Copy number changes of HMMR/RHAMM, MMP13, p16INK4A/CDKN2A, and ITGB4 were observed in 46%, 43%, 39%, and 32%, respectively of the malignant tumors, implicating these genes in MPNST pathogenesis. Concomitant amplifications of HGF, MET, and PDGFRA genes were also revealed in MPNSTs, suggesting the putative role of p70S6K pathway in NF1tumor progression. Conclusions: This study highlights the potential of array CGH in identifying novel diagnostic markers for MPNSTs.Neurofibromatosis type 1 (NF1; OMIM # 162200) is a common autosomal dominant disorder with a prevalence of 1 in 3,000 individuals worldwide. The majority of individuals with NF1 develop benign dermal neurofibromas, and approximately one third have benign plexiform neurofibromas (1, 2). In 5% to 10% of NF1 patients, neurofibromas (predominantly plexiform) develop into malignant peripheral nerve sheath tumors (MPNST; ref. 3). Whereas approximately half of all MPNSTs in the general population occur in the context of NF1, the other 50% are sporadic in origin. To date, understanding of histogenesis and the molecular mechanisms leading to the malignancy in NF1 remains fragmentary.