Enrico Martin

278 Chapter 12 that adheres to international guidelines (EARL criteria) and still results in a significant proportion of false positives. Nevertheless, it is advisable to offer PET scans to NF1 patients with newly symptomatic and suspicious lesions on MRI. Future perspectives Although it is clear that MRI’s should be used in the characterization of nerve sheath tumors and there seems strong evidence that PET scans offer additional accuracy in NF1 patients, several questions remain unresolved. An ideal algorithm of MRI and PET characteristics to stratify lesions at high-risk of malignant transformation has yet to emerge in order to minimize biopsies and unnecessary resections. It may be that sporadic and NF1 patients require separate algorithms for MRI characterization as (ancient) schwannoma’s are more common among non-NF1 patients. For PET-scans, ideal semi-quantitative features should be validated in a cohort that was scanned under a PET scan complying with EARL criteria. Diffusion weighted imaging and apparent diffusion coefficient mapping seem to be of true merit, but their incorporation in the diagnostic algorithm and possible replacement of PET scans needs further investigation. New imaging analyses such as radiomics are also interesting as radiomics has shown several purposes in other soft tissue sarcomas (STS) including distinction between benign and malignant as well as tumor grades. Yet no studies have been published using radiomics for nerve sheath tumors. Aggressive therapy for MPNST, quo vadimus? Radiotherapy Chapter 2-4 offered us further insight to survival outcomes of large cohorts of MPNST patients. An association of chemotherapy or radiotherapy use with survival was not observed in any of the cohorts studied. This is in line with previous literature and partially the reason for practice variation seen in Chapter 2-4 . However, these findings should be interpreted with caution as this thesis focused on overall survival only. MPNSTs have one of the highest rates of recurrence and metastasis in both adult STS and pediatric non-rhabdomyosarcoma STS (NRSTS). 6,7 Radiotherapy does decrease rates of local recurrences in microscopically positive margins and possibly in large tumors as well. 8–10 These indications are seemingly followed by most surgeons as seen in Chapter 5 . MPNSTs nevertheless do recur even in cases that have completely been resected and received radiotherapy. Additional caution should be taken for its administration in children. The European Pediatric Soft Tissue Sarcoma Study Group (EpSSG) treatment guidelines do implement radiation, but dosages have been modified from adult dosages, which is not supported by solid evidence and thus the efficacy may possibly be limited. Rates of radiotherapy administration in both adult and pediatric NF1-associated MPNST do not differ from sporadic MPNST. There is currently no guideline to treat NF1 patients differently to sporadic patients, yet we do