SARC031: A Phase II Trial of Selumetinib and Sirolimus for Patients with Unresectable or Metastatic Malignant Peripheral Nerve Sheath Tumors (MPNST)

PURPOSE: Combined mTOR and MEK inhibition, critical components of the RAS effector pathway underlying the pathogenesis of neurofibromatosis type 1 (NF1)-related tumors, caused regression in a malignant peripheral nerve sheath tumor (MPNST) transgenic mouse model. The primary objective was to determine the clinical benefit rate in patients with unresectable/metastatic MPNST. PATIENTS AND METHODS: The study design was a multi-institutional, open-label, Simon two-stage, phase II study of the MEK inhibitor selumetinib and mTOR inhibitor sirolimus. Patients ≥12 years with histologically confirmed MPNST received selumetinib 50 mg twice daily and sirolimus 4 mg once daily, in continuous 28-day cycles. Correlative studies evaluated patient-reported pain, immune signature in peripheral blood, and cell-free DNA (cfDNA). RESULTS: A total of 21 heavily pretreated patients [seven females; median age, 41 years (range, 16-72); and 14 with NF1] with advanced disease enrolled at five participating sites. Clinical benefit was observed in only one of seven in stage 1 and one of 14 patients in stage 2. The median number of cycles was two (range, 1-6). Most common adverse events (AE) were grade ≤2 gastrointestinal toxicity, acneiform rash, hypertriglyceridemia, mucositis, and transaminase elevation. Unlike the preclinical model, early 18F-fluorodeoxyglucose PET scan performed during cycle 1 demonstrated partial metabolic responses in five patients (24%), but these did not correlate with objective responses after cycle 2. cfDNA was able to detect MPNST with the potential to be a biomarker of response. CONCLUSIONS: The combination was safe, with manageable and expected AEs, but did not meet study parameters for further evaluation in MPNST. Correlative studies were informative and may guide future therapeutic trials of MPNST.