Real-world experience of larotrectinib in children, adolescents and young adults with TRK fusion solid tumors in France.

10056 Background: Larotrectinib is an FDA and EMA approved TRK inhibitor for TRK fusion solid tumors in patients with locally advanced or metastatic disease, or where surgical resection is likely to result in severe morbidity. Here we report the real-world activity and safety data on compassionate use and post-marketing authorization of larotrectinib collected in the SACHA-France study (NCT04477681), following the French Health Technology Assessment institution (HAS) request. Methods: All larotrectinib prescriptions made in France outside clinical trials since April 2019 for patients’ < 25 years-old were registered in the SACHA-France study. Safety and activity data were collected, with data cut-off of 23/01/2024. SACHA-France is open in all 31 French Society of Pediatric Oncology (SFCE) centers, it is approved as a real-world data source by the HAS and supported by the French National Agency for the Safety of Medicines and Health Products (ANSM). Results: 21 patients were included (4 compassionate use, 17 post-marketing authorization). Main cancer types were soft-tissue sarcomas (n=13, of them 7 infantile fibrosarcoma), followed by central nervous system (CNS) tumors (n= 7), and other solid extra-CNS tumors (n=1). All patients except one had a TRK fusion tumor: NTRK3 (n=10), NTRK2 (n=6, all CNS tumor) and NTRK1 (n=4). Median age at start of larotrectinib was 2.8 years (range: 0.2 -21.1). Ten patients had received no prior systemic therapy. Main reasons to start larotrectinib were to avoid mutilating surgery (n=9) and disease progression (n=9). Best objective response was reported as partial response in 13 out of 19 patients with evaluable disease (10/12 patients with soft tissue sarcomas, 2/6 patients with CNS tumors), with median time to response of 57 days. Of them, five patients with soft tissue sarcomas achieved a complete response after non mutilating surgery. Median treatment duration was 219 days (range: 10-1368, 5 patients still on therapy). Seven patients with soft tissue sarcomas stopped larotrectinib, after a median duration of 242 days (range: 122-1190), three of them after tumor surgery; none presented with tumor recurrence (follow-up: 350 days; range 40-636). At data cut-off, 8 patients had disease progression on-therapy (5/7 CNS tumors, 3/13 soft tissue sarcomas), with a NTRK resistance mutation identified in 2 out 3 patients with tumor biopsy. Adverse drug reaction (ADR) were reported in 2/21 patients (9%), including a grade 2 weight gain and a grade 3 neutrophil count decreased (1 patient each). Both ADRs were expected and required neither corrective treatment nor action on larotrectinib. Conclusions: Our real-world data confirm the favorable safety profile of larotrectinib with rapid and durable tumor-agnostic efficacy.