Nickerson, Molly

Background Neurofibromatosis type 1 (NF1) is a genetic disorder in which plexiform neurofibromas (PNs) develop in approximately 30% to 50% of affected individuals, often causing substantial morbidity. Treatment of NF1-associated PNs is challenging due to disease variability and tumor complexity. Observations In the Phase 2b ReNeu trial (NCT03962543), mirdametinib, a mitogen-activated protein kinase kinase 1/2 (MEK) inhibitor, demonstrated efficacy and a manageable safety profile in children and adults with symptomatic PNs, achieving confirmed objective responses in 52% of children and 41% of adults, with substantial reductions in target tumor PN volume and improvements in patient- and parent proxy-reported outcomes. However, dermatologic adverse events (AEs) are common with MEK inhibitors, including mirdametinib, and can impact adherence and quality of life. While the ReNeu protocol included supportive care considerations for skin reactions associated with mirdametinib, some investigators recognized a need for more detailed guidance. The ReNeu Scientific Steering Committee, in collaboration with oncology and oncodermatology experts, developed expert-driven recommendations for the proactive management of mirdametinib-related skin AEs. Conclusions These strategies emphasize early recognition, individualized care, and timely intervention to help reduce the severity of mirdametinib-related skin AEs, minimize dose modifications, and support treatment continuity and long-term treatment goals. Although these recommendations were specifically developed for mirdametinib based on ReNeu trial experience, they may also provide practical guidance for managing skin AEs associated with other MEK inhibitors in clinical practice.

Abstract BACKGROUND Mirdametinib, a MEK1/2 inhibitor, is the first FDA-approved medicine for both adults and children (≥2y) with NF1-PN not amenable to complete resection. In the phase 2b ReNeu trial (NCT03962543), confirmed objective response rate (ORR) was 41% in adults and 52% in children. This analysis explored relationships between baseline characteristics and mirdametinib responses in ReNeu. METHODS Confirmed ORR was the proportion of patients with ≥20% reduction from baseline in target PN volume by magnetic resonance imaging on consecutive scans during the 24-cycle treatment phase (“responders”) as assessed by blinded independent central review. Characteristics included age, body surface area (BSA), sex, race, ethnicity, target PN location, PN type (typical, nodular, or solitary nodular), target PN volume, and progression status. Rates of dose reductions and treatment-related adverse events (TRAEs) were evaluated. These factors were descriptively analyzed for potential relationships with confirmed objective response (data cutoff: 20September2023). RESULTS With mirdametinib, there was no clear difference between responders (n=53) and non-responders (n=61) in age (mean, 22.89 and 22.67y), BSA (mean, 1.42 and 1.51 m2), sex (60.4% and 57.4% female), race (83.0% and 68.9% White), or ethnicity (83.0% and 85.2% non-Hispanic/Latino). The majority of responders and non-responders had head/neck for target PN location (50.9% and 47.5%), typical PN type (81.1% and 63.9%), and baseline progression status (60.4% and 55.7%). Mean (95% CI) target PN volume was 283.43 (155.19, 411.66) and 415.74 (211.71, 619.77) mL, respectively. Dose reduction (11.3%; 18.0%) and TRAE rates (96.2%; 96.7%) were comparable. CONCLUSIONS This analysis suggests mirdametinib provides clinical benefit across a broad range of patient and NF1-PN tumor characteristics; a relationship between analyzed baseline characteristics and confirmed objective response was not established. Mean PN volume was higher in non-responders, though CIs overlapped. Dose reductions and emergence of TRAEs did not appear to impact response to mirdametinib. SUPPORT SpringWorks Therapeutics, Inc.

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.

Abstract ReNeu (NCT03962543) is a trial of the investigational, oral, selective MEK1/2 inhibitor (MEKi) mirdametinib in adults (≥18 years) and children (2-17 years) with NF1-PN. Skin adverse events (AEs) were common in ReNeu, and some discontinuations were noted with low-grade AEs. A multidisciplinary team retrospectively reviewed skincare practices at one high-enrolling site (n=12) with no discontinuations due to skin AEs; these were incorporated into ReNeu trial recommendations and recently updated. The purpose was to prevent/manage skin AEs and maintain protocol treatment adherence. MEKi skin AEs vary by pubertal status, therefore recommendations also vary by pubertal status. All patients were counseled to adopt hygienic skincare practices, including bathing daily, and using mild cleansers and hypoallergenic skin moisturizers (cream or ointment-based emollient; minimum BID) to prevent dry skin. Prepubescent patients were advised to incorporate diluted bleach baths (3-4 times/week) when initiating mirdametinib or after rash development. Treatments recommended for mild-to-severe dermatitis were hydrocortisone cream (2.5% BID) on face/skinfold areas and triamcinolone ointment (0.1% BID) on trunk/extremities. Treatments for mild acneiform eruptions included topical clindamycin lotion (1.0% BID) until resolution, with optional hydrocortisone cream (2.5% BID). For moderate-to-severe acneiform eruptions, cephalexin (20 mg/kg/day divided BID, max 500 mg, ≤6 weeks), amoxicillin (25 mg/kg/day divided BID, max 875 mg, ≤6 weeks), or oral fluconazole (20 mg/kg/day, max 100 mg, 5 days then once weekly for 3 months) were suggested. Postpubescent patients were advised to initiate topical 1.0% clindamycin lotion and oral doxycycline or minocycline (50-mg daily, 3 months) with mirdametinib initiation. Patients with subsequent mild-to-severe acneiform eruptions were advised to apply hydrocortisone cream (2.5% BID) or triamcinolone ointment (0.1% BID). Referral to a dermatologist was suggested for all patients with uncontrolled dermatitis, worsening acneiform eruptions, or infection. Proactive skincare practices appeared effective at this site, but prospective validation is necessary before making clinical recommendations.

Abstract BACKGROUND Patients with NF1-PN in the phase 2b ReNeu trial (NCT03962543) of mirdametinib in adults (N=58, ≥18y) and children (N=56, 2-17y) had a deeper median (range) best reduction (adults: -41% [-90% to 13%]; children: -42%, [-91% to 48%]) from baseline in target PN volume than previously published in trials of other agents in NF1-PN. METHODS In the 24-cycle (1-cycle=28d) treatment phase, objective response rate (ORR) was the percentage with confirmed objective responses (OR) of ≥20% target PN volume reduction from baseline on consecutive MRIs (by blinded independent central review). This analysis includes patients achieving deep response (>50% best reduction from baseline in target PN volume) regardless of OR and inclusive of patients in the long-term follow-up. Exploratory analysis of baseline characteristics compared patients with deep response and patients with ≤50% volume reduction. RESULTS ORR was 41% (24/58) in adults and 52% (29/56) in children treated with mirdametinib. 62% (15/24) of adults and 52% (15/29) of children who achieved OR had deep response. To further characterize deep response, 2 adults and 3 children with deep response without confirmation or in long-term follow-up were included. Of those with a deep response, 35% (6/17) of adults and 72% (13/18) of children were investigator-defined as having progressing PN. Patients achieved deep response regardless of baseline age, sex, target PN volume, tumor location, or progression status. For adults and children, median time to best percent change from baseline in PN volume for patients achieving deep response was 25.4 and 21.8mo; for patients with reductions of ≥20% to ≤50% was 15.3 and 15.2mo; for patients with reductions of <20% was 7.8 and 4.2mo, respectively. CONCLUSIONS Patients had a similar likelihood of achieving deep response across assessed baseline characteristics. A trend between deep response and longer treatment duration suggests a benefit of prolonged therapy with mirdametinib.