Neurofibromatosis type 1 (NF1) is a frequent, autosomal dominant disorder caused by heterozygous mutations (intragenic or microdeletion) of the NF1 tumor suppressor gene (chr.17q11.2). One of the clinical features is the development of benign and malignant tumors. The most common benign tumors in these patients are tumors of the peripheral nerve sheath, named neurofibromas (cutaneous, subcutaneous and plexiform). Every NF1 patient has a life time risk of 8 to 13% of developing a malignant peripheral nerve sheath tumor (MPNST) out of a pre-existing neurofibroma. In patients with a NF1 microdeletion (5% of NF1 patients), this risk is even twice as high compared to patients with an intragenic mutation. MPNSTs lead to a bad prognosis for the patient, with an overall five-year survival of less than 25%. To know more about the development and progression of these tumors, they will be screened by microarray comparative genome hybridization (Leuven) and full exome sequencing (Leuven). Further experiments will be done in cooperation (bidirectional) with the foreign labs of Victor Mautner (Germany), André Bernards (USA), Karen Cichowski (USA) and Yuan Zhu (USA).