SpringWorks Therapeutics, Inc. announced that four abstracts from the company's portfolio will be presented at the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting being held May 31 to June 4, 2024. Data from the pivotal Phase 2b ReNeu trial evaluating mirdametinib, an investigational MEK inhibitor, in adults and children with neurofibromatosis type 1-associated plexiform neurofibromas (NF1-PN) will be presented in an oral presentation. ReNeu is the multicenter trial conducted to date in patients with NF1-PN, a condition in which tumors can grow aggressively along peripheral nerves and lead to pain, disfigurement and other morbidities.

In the ReNeu trial, mirdametinib treatment demonstrated deep and sustained tumor volume reductions, and improvement in pain and health-related quality of life across both the adult and pediatric cohorts. In addition, three new data sets from the pivotal Phase 3 DeFi trial of nirogacestat in adults with desmoid tumors will be presented at ASCO. Monitoring ovarian function in oncology studies and the onset and resolution of ovarian toxicity for desmoid tumor patients treated with nirogacestat in the DeFi trial will be discussed in an oral presentation.

Investigators will also present two posters that include post hoc analyses from the DeFi trial in high-risk patient populations, which reinforce the efficacy and safety of nirogacestat in adults with desmoid tumors across various clinical characteristics. As previously reported, results from the pivotal Phase 2b ReNeu trial (NCT03962543) demonstrated a statistically significant confirmed objective response rate (ORR), the primary endpoint of the study, as well as deep and sustained reduction in tumor volume and significant improvement in key secondary patient-reported outcome measures in both adults and children with NF1-PN. The data being presented at ASCO include: As of the data cutoff of September 20, 2023, mirdametinib treatment resulted in a confirmed ORR of 41% (24/58; P<0.001) in adults and 52% (29/56; P<0.001) in children, as assessed by blinded independent central review (BICR).

Two additional adult patients and one additional pediatric patient had a confirmed partial response in the long-term follow-up phase. Tumor volume reductions were deep and durable over the course of the study. Median (range) best change in tumor volume from baseline was -41% (-90% to 13%) in adults and -42% (-91% to 48%) in children.

Among study participants with a confirmed objective response on mirdametinib, 62% of adults and 52% of children achieved a >50% reduction in tumor volume. The median treatment duration for both adults and children was 22 months; the median (range) time to onset of response was 7.8 months (4 to 19 months) in adult patients and 7.9 months (4 to 19 months) in pediatric patients; the median duration of response was not reached in either group. Both adult and pediatric patients experienced improvement in patient-reported pain and patient-reported (adult) or patient- or parent proxy-reported (children) health-related quality of life (HRQoL) at the pre-specified Cycle 13 assessment.

Least square (LS) mean change from baseline at Cycle 13 in worst tumor pain (assessed by Numeric Rating Scale-11) was -1.3 (P<0.001) in adults and -0.8 (P=0.003) in children. LS mean change from baseline at Cycle 13 in HRQoL was 3.9 in adults (P=0.018) and 4.0 (P=0.096) as self-reported in children; parent-proxy reported LS mean change in HRQoL in children was 5.6 (P=0.005). Mirdametinib was generally well tolerated in the ReNeu trial, with most adverse events (AEs) being Grade 1 or 2. Among all study participants, 21% of adults and 9% of children discontinued the study due to treatment-related adverse events (TRAEs), and dose reductions due to TRAEs were 17% in adults and 12% in children.

The most frequently reported TRAEs affecting >20% of adult participants were dermatitis acneiform, diarrhea, nausea, vomiting, and fatigue. The most frequently reported TRAEs affecting =20% of pediatric participants were dermatitis acneiform, diarrhea, paronychia (infection of the tissue adjacent to a fingernail or toenail), nausea, decrease in ejection fraction (asymptomatic), and increase in blood creatinine phosphokinase (asymptomatic). The most frequently reported TRAEs affecting >20% of adult participants were dermatitis acneiform, diarrhea, nausea, vomiting, and fatigue.

The most frequently reported TRAEs affecting =20% of pediatric participants were dermatitis acneiform, diarrhea, paronychia (infection of the tissue adjacent to a fingernail or toenail), nausea, decrease in ejection fraction (asymptomatic), and increase in blood creatinine phosphokinase (asymptomatic). A post hoc analysis of the DeFi trial was conducted to assess the effect of nirogacestat in subgroups of patients with desmoid tumors who have risk factors associated with poor prognosis (i.e., larger tumor size, younger age, CTNNB1 gene mutation, and presence of pain at baseline). Nirogacestat demonstrated consistent improvements in progression-free survival (PFS) and ORR versus placebo in patients with these poor prognostic factors.

These results were consistent with the overall DeFi patient population and suggest that nirogacestat can provide clinically meaningful benefit in patients with characteristics that have been historically associated with poor prognosis.