2058 - Outcomes Associated with Radiation Therapy for Localized Malignant Peripheral Nerve Sheath Tumors (MPNST)

02:30pm - 04:00pm PT

Hall F

Screen: 31

POSTER

Presenter(s)

Victoria Doss, MD - Johns Hopkins Medicine, Baltimore, MD

V. L. Doss¹, E. Burnett¹, L. Zhang², H. C. Wilbur², B. Lindsey³, C. A. Pratilas², and S. Acharya¹; ¹Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, ²Department of Oncology, Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University School of Medicine, Baltimore, MD, ³Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore, MD

Purpose/Objective(s): MPNST are rare, aggressive soft tissue sarcomas (STS) with highest incidence in patients with Neurofibromatosis type 1 (NF1). Recurrence rate is high even with negative margin resection. While radiation therapy (RT) reduces local recurrence in many STS, data on MPNST are limited, and concerns about RT-associated secondary malignancies persist, especially in patients with NF1. This study analyzed overall survival (OS), progression-free survival (PFS) and local failure (LF) in localized MPNST treated with or without RT, as well as secondary malignancies and their relation to the RT field.

Materials/Methods: Patients with localized MPNST diagnosed between 2010 and 2024 were retrospectively identified from our institutional sarcoma database. Exclusion criteria included: metastatic disease at diagnosis, follow up less than three months, missing RT data and/or non-curative intent therapy. Survival was estimated using Kaplan-Meier method. Effect of confounding variables was assessed using Cox proportional hazards. Cumulative incidence of LF was analyzed using competing risks.

Results: Sixty patients met inclusion criteria. Median age at diagnosis was 32.5 years, and 45 patients (75%) had NF1. Median follow-up for the entire cohort was 3.7 years (range 0.52 – 14.4 years). Median tumor size was 7.2cm. Surgical resection was performed in 58 patients (96.7%), of whom 16 patients (27.5%) had positive margins. Chemotherapy was administered to 34 patients (56.7%). RT was delivered in 36 patients (60%) with a median equivalent 2Gy dose of 50Gy (a/b = 4), most often preoperatively (63%). RT vs no RT groups had no difference in tumor size, margin status or NF1 status (all p>0.05). RT was associated with improved OS (3-yr OS: 48% vs. 88.5%, p=0.04) and PFS (3-yr PFS: 41.6% vs. 62.8%, p=0.011). Tumor size and positive margins were also associated with OS and PFS. On multivariate analysis, RT remained associated with improved OS (HR=0.36, 95% CI: 0.15-0.85, p=0.020) after adjusting for tumor size (HR=1.20, 95% CI: 1.07-1.34, p=0.001) and positive margins (HR=2.45, 95% CI: 1.10-5.45, p=0.029). RT also remained significantly associated with improved PFS (HR=0.31, 95% CI: 0.15-0.65, p=0.002) after adjusting for tumor size (HR=1.16, 95% CI: 1.06-1.27, p=0.002) and positive margins (HR=2.11, 95% CI: 1.05-4.21, p=0.035). The 12-month cumulative incidence of LF with vs without RT was 8.3% [95% CI: 2.1 - 20%] vs 33.3% [95% CI: 15.9 – 51.8%]. Seven patients (11.7%) developed secondary malignancies, none of which were in the RT field. Secondary malignancies included four de novo MPNST, one astrocytoma, one gastrointestinal stromal tumor, and one chemotherapy-related acute myeloid leukemia.

Conclusion: In this cohort of patients with localized MPNST, RT is independently associated with improved PFS and OS. There were no secondary malignancies in the RT field.