Research protocol All NF1 patients are linked to the UZ Leuven. Their follow-up is done by Prof. Dr. Eric Legius. When the patient is suspected of having a MPNST, the patient is referred to the surgeon of the clinical oncology department, respectively. Also neurofibromas are removed when they are causing problems for the patient. As part of the different tumor care programs in our hospital, a tumor piece is sent from pathology to the centre for human genetics for routine genetical analysis, like karyotyping. In the lab for neurofibromatosis research, the rest material is frozen as tumor pieces and as dissociated cells for research purposes. The samples are stored in a database system that is accessible only for the neurofibromatosis research group. In cooperation with the group of Victor Mautner and Karen Cichowski, the tumor database was further completed with NF1 tumor material and cell lines. The latter samples were coded and could be used as part of our collaboration.