Maraka, Stefania

Abstract BACKGROUND Mirdametinib is the first FDA-approved MEK1/2 inhibitor for both adults and children (≥2y) with symptomatic NF1-PN. In ReNeu, symptomatic improvement and PN volume reductions were observed at the earliest assessments (~91 and ~152 days, respectively) and were sustained. This analysis evaluated time to first onset and resolution of commonly reported TRAEs in the ReNeu trial. METHODS Data cutoff (DCO) was September 20, 2023. Median time to first onset and resolution (days) for common TRAEs (≥15%) were evaluated for prepubescents (≥2 to <12y, n=32), postpubescents (≥12 to <18y, n=24), younger adults (≥18 to ≤50y, n=48), and older adults (>50y, n=10). RESULTS Common TRAEs were mostly grades 1 to 2 (83%). In prepubescents, median day (range) of onset was 32 (14, 263) for vomiting, 71 (19, 386) for dermatitis acneiform, 123 (1, 663) for diarrhea, 124 (52, 775) for paronychia, and 127 (2, 663) for nausea. For postpubescents, median day (range) of onset was 8 (1, 438) for diarrhea, 8 (2, 574) for nausea, 12 (1, 252) for dermatitis acneiform, 28 (2, 354) for vomiting, and 110 (43, 245) for paronychia. In younger adults, median day (range) of onset was 5 (1, 352) for nausea, 8 (2, 15) for dermatitis acneiform, 9 (2, 73) for diarrhea, and 29 (1, 264) for vomiting. For older adults, median day (range) of onset was 4 (1, 286) for diarrhea, 9 (2, 15) for nausea, and 13 (2, 38) for dermatitis acneiform. Time to resolution was variable between TRAEs and among patients in all age groups; 90% resolved completely by DCO. Among all patients, 18 had a TRAE of asymptomatic ejection fraction decrease, with all but one resolving by DCO. CONCLUSIONS Overall, common TRAEs arose before treatment benefits and were generally resoluble by DCO. Proactively managing TRAEs may improve treatment experience and adherence.

PURPOSE Pharmacologic therapies for neurofibromatosis type 1-associated plexiform neurofibromas (NF1-PNs) are limited; currently, none are US Food and Drug Administration–approved for adults. METHODS ReNeu is an open-label, multicenter, pivotal, phase IIb trial of mirdametinib in 58 adults (≥18 years of age) and 56 children (2 to 17 years of age) with NF1-PN causing significant morbidities. Patients received mirdametinib capsules or tablets for oral suspension (2 mg/m 2 twice daily, maximum 4 mg twice daily), regardless of food intake, in 3 weeks on/1 week off 28-day cycles. The primary end point was confirmed objective response rate (ORR; proportion of patients with a ≥20% reduction of target PN volume from baseline on consecutive scans during the 24-cycle treatment phase) assessed by blinded independent central review (BICR) of volumetric magnetic resonance imaging. RESULTS Twenty-four of 58 adults (41%) and 29 of 56 children (52%) had a BICR-confirmed objective response during the 24-cycle treatment phase; in addition, two adults and one child had confirmed responses during long-term follow-up. Median (range) target PN volumetric best response was –41% (−90 to 13) in adults and –42% (−91 to 48) in children. Both cohorts reported significant and clinically meaningful improvement in patient- or parent proxy-reported outcome measures of worst tumor pain severity, pain interference, and health-related quality of life (HRQOL) that began early and were sustained during treatment. The most commonly reported treatment-related adverse events were dermatitis acneiform, diarrhea, and nausea in adults and dermatitis acneiform, diarrhea, and paronychia in children. CONCLUSION In ReNeu, the largest multicenter NF1-PN trial reported to date, mirdametinib treatment demonstrated significant confirmed ORRs by BICR, deep and durable PN volume reductions, and early, sustained, and clinically meaningful improvement in pain and HRQOL. Mirdametinib was well-tolerated in adults and children.