Every NF1 patient has a life time risk of 8 to 13% to develop a malignant peripheral nerve sheath tumor (MPNST) out of a pre-existing (plexiform) neurofibroma. This risk is even twice as high for NF1 microdeletion patients compared to patients with an intragenic mutation. MPNSTs are difficult to diagnose in early phase because of the large number of tumors and diverse locations. These tumors infiltrate easily in surrounding tissue and frequently give rise to metastases. At this moment, the only available treatment is surgical removal of these MPNSTs. Complete resection is often difficult due to the size of the tumors and the location on important nerves. The five-year survival of patients with MPNSTs is less than 25%.