Background: Neurotrophic tyrosine receptor kinase (NTRK) gene fusions are oncogenic drivers in various tumor types, including central nervous system (CNS) tumors. Larotrectinib is a first-in-class, highly selective TRK inhibitor approved for the treatment of adult and pediatric patients with TRK fusion cancer, with an objective response rate (ORR) of 78% across 175 adult and pediatric patients with various non-CNS cancers (McDermott et al, ESMO 2020). We report data on patients with TRK fusion-positive primary CNS tumors. Methods: Patients with primary CNS tumors harboring an NTRK gene fusion enrolled in two clinical trials (NCT02637687, NCT02576431) were identified. Larotrectinib was administered until disease progression, withdrawal, or unacceptable toxicity. Response was investigator assessed. Results: As of July 2020, 33 patients with TRK fusion-positive CNS tumors were identified: 19 high-grade gliomas (HGG), 8 low-grade gliomas (LGG), 2 glioneuronal tumors, 2 neuroepithelial tumors, 1 CNS neuroblastoma, and 1 small round blue cell tumor. The patients had gene fusions involving NTRK2 (n = 24; 73%), NTRK1 (n = 5; 15%), and NTRK3 (n = 4; 12%). Median age was 8.9 years (range 1.3–79.0); 26 patients were pediatric ( < 18 years). Patients were heavily pre-treated with 45% having 2 or more prior lines of systemic therapy. The ORR in all patients was 30% (95% CI 16–49): 3 complete responses (all in pediatric patients), 7 partial responses (2 pending confirmation), 20 stable disease (including 15 pts > 6 months), and 3 progressive disease. The ORR in patients with HGG and LGG were 26% (95% CI 9–51) and 38% (95% CI 9–76), respectively. In all patients, the 24-week disease control rate was 73% (95% CI 54–87). Twenty-three of 28 patients (82%) with measurable disease had tumor shrinkage. The median time to response was 1.9 months. Median duration of response (DoR) was not reached (95% CI 3.8–not estimable [NE]) at a median follow-up of 12.0 months. The 12-month DoR rate was 75% (95% CI 45–100). Median PFS was 18.3 months (95% CI 6.7–NE) at a median follow-up of 16.5 months. Median overall survival (OS) was not reached (95% CI 16.9–NE) at a median follow-up of 16.5 months, with a 12-month OS rate of 85% (95% CI 71–99). Duration of treatment ranged from 1.2 to 31.3+ months. Treatment-related adverse events (TRAE) were reported by 20 patients and were Grade 3–4 in 3 patients (9%). There were no treatment discontinuations due to TRAEs. Conclusions: In patients with TRK fusion-positive CNS tumors, larotrectinib demonstrated rapid and durable responses, high disease control rate, and a favorable safety profile. These results support testing for NTRK gene fusions in patients of all ages with CNS tumors. Clinical trial information: NCT02637687, NCT02576431