SpringWorks Therapeutics’ mirdametinib shows efficacy in Phase 2b NF1-PN trial

SpringWorks Therapeutics announced positive topline results from the pivotal Phase 2b ReNeu trial evaluating mirdametinib, an investigational MEK inhibitor, in pediatric and adult patients with neurofibromatosis type 1-associated plexiform neurofibromas, or NF1-PN. The ReNeu trial enrolled 114 patients. The primary endpoint was confirmed objective response rate – ORR -. As of September 20, 52% of pediatric patients and 41% of adult patients had BICR confirmed objective responses within the 24-cycle treatment period. An additional pediatric patient and two additional adult patients achieved confirmed objective responses after Cycle 24 in the long-term follow up phase of the trial. Median best percent change from baseline in target tumor volume was -42% and -41% in the pediatric and adult cohort, respectively. As of the data cut-off, the median duration of treatment was 22 months in both the pediatric and adult cohorts. Median duration of response was not reached in either cohort. Pediatric and adult patients in the ReNeu trial also experienced statistically significant improvements from baseline in pain, quality of life, and physical function, as assessed across multiple patient-reported outcome tools. Mirdametinib was generally well tolerated in the ReNeu trial, with the majority of adverse events being Grade 1 or Grade 2. The FDA and the European Commission have granted Orphan Drug designation for mirdametinib for the treatment of NF1. SpringWorks plans to submit a New Drug Application for mirdametinib to the FDA in the first half of 2024.