Enrico Martin

51 Abstract Background Despite curative intents of treatment in localized malignant peripheral nerve sheath tumors (MPNST), prognosis remains poor. This study investigated survival and prognostic factors for overall survival in non-retroperitoneal and retroperitoneal MPNSTs in the Netherlands. Methods Data were obtained from the Netherlands Cancer Registry and the Dutch Pathology Database. All primary MPNSTs were collected. Pediatric cases (age ≤18 years) and synchronous metastases were excluded from analyses. Separate Cox proportional hazard models were made for retroperitoneal and non-retroperitoneal MPNSTs. Results A total of 629 localized adult MPNSTs (35 retroperitoneal cases, 5.5%) were included for analysis. In surgically resected patients (88.1%), radiotherapy and chemotherapy were administered in 44.2% and 6.7% respectively. In retroperitoneal cases significantly less radiotherapy and more chemotherapy were applied. In non- retroperitoneal MPNST, older age (60+), presence of NF1, size >5cm, and deep-seated tumors were independently associated with worse survival. In retroperitoneal MPNST male sex and age 60+ years old were independently associated with worse survival. Survival of R1 and R0 resections were similar for any location, while R2 resections were associated with worse outcome. Radiotherapy and chemotherapy administration were not associated with survival. Conclusion In localized MPNST, risk stratification for survival can be done using several patient- and tumor specific characteristics. Resectability is the most important predictor for survival in MPNST. No difference is present between R1 and R0 resections in both retroperitoneal and non-retroperitoneal MPNSTs. The added value of radiotherapy and chemotherapy is unclear. 3