CTNI-07. LONG-TERM EFFICACY AND SAFETY OF LAROTRECTINIB IN PATIENTS WITH TRK FUSION PRIMARY CENTRAL NERVOUS SYSTEM (CNS) TUMORS: AN UPDATED ANALYSIS

Abstract BACKGROUND Larotrectinib is a highly selective TRK inhibitor approved for TRK fusion tumor-agnostic use. We report updated data on larotrectinib-treated patients with TRK fusion primary CNS tumors. METHODS Patients enrolled in 2 clinical trials (NCT02637687 [SCOUT], NCT02576431 [NAVIGATE]) were included. Responses were independent review committee (IRC)-assessed (RANO). Patients from SCOUT could stop larotrectinib in the absence of on-treatment progression (wait-and-see). Data cutoff: July 2023. RESULTS Fifty-five patients (38 aged <18 years at enrolment) were evaluated, including 16 with non-measurable disease at baseline. Tumor histologic groups included: high-grade glioma (HGG; n=32), low-grade glioma (LGG; n=15), and other (n=8). For all patients (n=55), ORR was 27% (95% CI 16-41): 3 CR, 12 PR, 24 SD (15 for >24 weeks), 12 PD, and 4 not evaluable. For pediatric patients (n=38), ORR was 37% (95% CI 22-54). ORR in patients with measurable disease only was 38% (95% CI 23-55) for all patients (n=39) and 52% (95% CI 32-71) for pediatric patients (n=27). The 24-week disease control rates were 55% (95% CI 41-68) and 74% (95% CI 57-87) for all patients and pediatric patients, respectively. Median time to response, DoR, PFS, and OS were 2, 12 (95% CI 6-not estimable [NE]), 12 (95% CI 7-20), and 38 months (95% CI 23-NE), respectively. Treatment duration ranged from 1 to 64+ months. At data cutoff, 1 pediatric patient with HGG and 4 with LGG entered wait-and-see; median duration of first wait-and-see period was 20 months (range 4-29). One pediatric patient with LGG resumed treatment following disease progression in wait-and-see. Treatment-related adverse events were predominantly Grade 1/2. CONCLUSION Larotrectinib demonstrated rapid, durable responses and manageable safety in patients with TRK fusion primary CNS tumors. This supports the adoption of NGS panels containing NTRK gene fusions when testing patients to identify those who might benefit from TRK inhibitor therapy.