RADT-20. HISTOPATHOLOGIC FINDINGS IN MALIGNANT PERIPHERAL NERVE SHEATH TUMOR ARE BOTH PROGNOSTIC FOR OVERALL SURVIVAL AND PREDICTIVE FOR RESPONSE TO RADIATION THERAPY

Abstract

Abstract BACKGROUND Malignant peripheral nerve sheath tumor (MPNST) is an aggressive neoplasm associated with neurofibromatosis type 1 (NF1). Despite multimodal therapy, clinical outcomes remain poor. To elucidate markers of MPNST treatment response, we retrospectively reviewed the medical records of MPNST patients at a single institution and performed histopathological and immunohistochemical (IHC) analysis for predictive and prognostic features. METHODS We identified 54 consecutive patients treated at University of California San Francisco between 1990 and 2018 that met diagnostic criteria for MPNST on pathologic review with sufficient tissue available for histology and immunohistochemistry (IHC) assays. IHC was performed for Ki-67, EGFR, p53, H3K27me3, neurofibromin, S100, p75NTR, SOX10, p16, and SOX2. Overall survival (OS), metastasis free survival (MFS), and locoregional failure free rate (LFFR), were estimated using the Kaplan-Meier method. Log-rank test, Cox Proportional Hazards regression, and hierarchical clustering were performed in R. RESULTS With a median follow up of 19.2 months, the 5-year OS, MFS, and LFFR were 58%, 68%, and 66%, respectively, with no significant differences between NF1 associated (n=32) and sporadic tumors (n=22). Radiation therapy significantly improved 5-year LFFR (80% versus 49%, p=0.05), but not OS or MFS. Tumor grade was associated with worse OS by Fédération Nationale des Centres de Lutte Contre Le Cancer (FNCLCC) grading (p=0.02). Furthermore, elevated Ki-67 index was associated with worse 5-year OS (39% versus 73% for Ki-67 index ³ 60 and Ki-67 index < 60, p=0.01). Finally, hierarchical clustering of IHC data identified a predictive signature defined by elevated Ki-67 and EGFR expression associated with improved responses to radiation therapy (5-year OS 86% versus 10%, p=0.004). CONCLUSIONS Our data provide insights into the diagnosis and treatment of MPNST. Additional investigation is needed to understand the biologic mechanisms and generalizability of the signatures uncovered in our analysis.