ReNeu: A pivotal phase 2b trial of mirdametinib in children and adults with neurofibromatosis type 1 (NF1)-associated symptomatic inoperable plexiform neurofibroma (PN).

3016 Background: PN in patients (pts) with NF1 can cause pain, disfigurement, impaired quality of life (QoL), and can undergo malignant transformation. ReNeu (NCT03962543), a multicenter, open-label, Phase 2b study, evaluated efficacy and safety of the highly selective, oral, investigational MEK1/2 inhibitor mirdametinib in adult (≥18 y) and pediatric (2-17 y) pts with inoperable NF1 PN causing significant morbidities. Methods: Mirdametinib was administered as a capsule or dispersible tablet (2 mg/m 2 BID, max 4 mg BID) without regard to food in 3 wk on/1 wk off 28-d cycles. The primary endpoint was confirmed objective response rate (ORR; percentage of pts with MRI-assessed ≥20% reduction of target PN volume by blinded independent central review BICR within the 24-cycle treatment phase). The minimum clinically relevant ORR (null) was defined as 23% for adults and 20% for pediatrics. Ptscould continue treatment in an optional long-term follow-up (LTFU) phase. Additional key endpoints were duration of response (DoR), time to response (TTR), change from baseline (BL) in target PN volume, pain severity (Numerical Rating Scale-11 NRS-11), pain interference (Pain Interference Index PII), health-related (HR) QoL (PedsQL), and safety. Results: All114 pts (58 adult, 56 pediatric) received mirdametinib. As of the 20 Sept 2023 data cutoff (DCO), BICR-confirmed ORR during the treatment phase was 41% (95% CI, 29-55; P<.001 vs null) in adults and 52% (95% CI, 38-65; P<.001 vs null) in pediatric pts. Two adult pts and 1 pediatric pt also had a confirmed response in the ongoing LTFU. Median (min, max) target PN volumetric best response from BL was -41% (-90, 13) and -42% (-91, 48) in adult and pediatric pts, respectively. As of the DCO, median treatment duration was 22 mo for each cohort and median DoR was not reached. Median (range) TTR was 7.8 (4-19) mo in adult pts and 7.9 (4-19) mo in pediatric pts. Adult and pediatric pts had statistically significant improvements from BL to cycle 13 in NRS-11, PII, and key PedsQL measures. Most frequent (≥35% pts) treatment-emergent adverse events (TEAEs) were dermatitis acneiform, diarrhea, nausea, and vomiting in adults and diarrhea, dermatitis acneiform, and vomiting in pediatric pts. 16% and 25% of adult and pediatric pts, respectively, had grade ≥3 treatment-related AEs, and 22% and 9%, respectively, discontinued due to TEAEs. Conclusions: In ReNeu, the largest multicenter NF1 PN trial reported to date, mirdametinib demonstrated a statistically significant ORR by BICR, with deep and durable PN volume reductions, significant improvements in pain severity, pain interference, and HRQoL, and a manageable safety profile in both adults and children. Together with a dispersible tablet formulation, these results underscore mirdametinib’s potential to become an important new treatment option for NF1 PN pts across all ages. Clinical trial information: NCT03962543 .