Enrico Martin

292 Resectability of the MPNST was the most important factor predicting worse survival in localized disease. In retroperitoneal MPNST, older age (60+), male gender, and irresectable tumors were associated with worse survival. In non-retroperitoneal MPNST truncal tumor site was not associated with worse survival which may suggest that this association observed in other studies may be driven by retroperitoneal tumors. Furthermore, there was no difference between an R0 and R1 resection on survival in both retroperitoneal and non-retroperitoneal MPNST. This is important as it indicates that MPNSTs are eligible for function-sparing surgery with planned microscopically positive margins. Chapter 4 Treatment and Survival in Pediatric MPNST Using the same databases as Chapter 3 , 70 pediatric patients were identified and investigated for treatment and survival. Pediatric MPNSTs are rare, treated by pediatric oncologists, and were found to be associated with increased survival in Chapter 2 , therefore prompting further investigation. We observed that pediatric patients presented with similar clinicopathologic features as adult MPNSTs. In NF1 children, tumors tended to be larger at time of diagnosis, but were generally treated similarly to sporadic patients. Presence of NF1 was the only clinicopathologic feature associated with worse survival in localized pediatric MPNST. In contrast to adult MPNST, we observed that prognosis for localized pediatric MPNST has ameliorated after 2005. This may be due to the centralization of pediatric cancer health care in the Netherlands as well as the implementation of doxorubicin and ifosfamide as standard chemotherapy regimens. The use of radiotherapy and chemotherapy were not found to be associated with survival in any population analyzed in Chapter 2-4 . Chapter 5 Oncological Treatment Considerations Because MPNSTs are rare and treated by several surgical subspecialties, variation in clinical decision-making may be present. Surgical oncologists treat MPNSTs as part of their sarcoma clinic, but peripheral nerve surgeons as a malignant form of nerve sheath tumors. By means of an international survey among several surgical societies, we evaluated how oncological treatment considerations varied as a whole and between surgical subspecialties. A total of 174 surgeons filled out the survey. Variation in cases and case load was evident between surgical subspecialties and surgical oncologists treated most patients. Diagnostic work-up differed between surgical subspecialties, but surgical oncologists adhered most commonly to sarcoma guidelines. (Pre) operative considerations for the preservation of function differed among all surgeons, many of which would not consider less extensive resections to preserve function. Indications for the use of radiotherapy did not differ between specialties, large tumor size (>10cm) and microscopically positive margins being the most common reasons for its administration. Sequence of administration differed significantly between specialties; surgical oncologists preferred neoadjuvant administration in contrast to other specialties. Indications for the use of chemotherapy in localized disease lacked