LAUSR

e22537 Background: MPNST accounts for about 5% of soft tissue sarcomas. It is known to have high metastatic potential and poor prognosis, but reported long-term outcomes vary widely across published series. Our study aimed to determine factors affecting clinical outcome in a large cohort of patients (pts) with MPNSTs treated at reference sarcoma center. Methods: 289 consecutive pts (144 woman and 145 man) referred, diagnosed and treated between 03/1998 and 04/2018 were analyzed. Kaplan-Meier estimator and the log-rank test were used in survival analysis and multivariate Cox proportional hazards model was used to confirm the correlation. Results: Mean age at diagnosis was 50y (15-86). 39 (13.5%) pts were NF1 positive, 12 were primary diagnosed with metastatic disease. After median follow-up of 66.5 months (m) (95% confidence interval, CI 58.1 – 85.2) 151 pts continue treatment or follow-up. Median OS was 55.7m (39.3 - 148.9) in the whole group while 5y survival rate was 48.8% (CI: 42.8-55.7%). 37/167 pts with radical resection in reference center developed local recurrence, and 75/92 pts operated first in regional hospitals. Median DFS was 29.7m (CI: 16.1-58.3) in case of treatment in reference center and 4.1m (CI: 2.4-9.2) in case of regional hospital (p < 0.001).72 pts developed metastatic disease and were treated with chemotherapy. Median PFS on 1st line was 5.6m (CI: 3.3 - 8.1), There were no statistically significant differences in survival rates nor in response rates between doxorubicin- and ifosfamid-based regiments. Tumor size at diagnosis (HR:2.33, CI: 1.50-3.62), high grade (HR:3.31, CI:2.14-5.12) and R0 resection (HR:0.47, CI:0.30-0.72) were the strongest independent predictors of DFS and OS. (neo)adjuvant radiotherapy did not influenced LRFS in case of R0 resection but improved LRFS when complete resection was not feasible (HR: 0.22 CI: 0.08-0.58 p = 0.002). Conclusions: MPSNT is a highly aggressive tumor with poor prognosis. High quality surgery remains the mainstay of management for these patients, but multimodal treatment should be considered in majority of cases in MDT units. There is unmet need for new therapies in advanced/metastatic cases.