Larotrectinib (laro) long-term efficacy and safety in patients (pts) with tropomyosin receptor kinase (TRK) fusion thyroid carcinoma (TC)

6091 Background: Neurotrophic tyrosine receptor kinase ( NTRK) gene fusions are oncogenic drivers in a variety of tumor types, including TC. Laro is a first-in-class, highly selective, central nervous system (CNS)-active TRK inhibitor approved for tumor-agnostic use in pts with TRK fusion cancer based on a rapid, robust, and durable objective response rate (ORR) in both adult and pediatric pts with various cancers. Here, we report data on the subset of pts with TRK fusion TC treated with larotrectinib with long-term follow-up. Methods: Pts with TRK fusion TC enrolled in three laro clinical trials (NCT02576431, NCT02122913, NCT02637687) were included. Laro was administered at 100 mg twice daily to most pts; two pediatric pts received 100 mg/m 2 . Responses were assessed per independent review committee (IRC) using RECIST v1.1. Data cut-off: July 20, 2022. Results: As of data cut-off, 30 pts were eligible for efficacy assessment by IRC. The median age was 61.5 years (range 6–80) and the median time since initial cancer diagnosis was 5.0 years (range 0–46). The gene fusions involved NTRK1 (n =14; 47%) or NTRK3 (n =16; 53%). Fifteen pts (50%) received no prior systemic therapies, and six (20%) received ≥2; 23 (77%) received prior radioiodine. ORR was 63% (95% confidence interval [CI] 44–80): three (10%) complete response, 16 (53%) partial response (PR), five (17%) stable disease, four (13%) progressive disease, and two (7%) not evaluable. For pts classified as differentiated TC (DTC; n = 23), the ORR was 78% (95% CI 56–93). For pts classified as anaplastic TC (ATC; n = 7), the ORR was 14% (95% CI 0–58). All four pts with CNS metastases at baseline had a PR. Median time to response was 1.9 months, and median duration of response (DoR) was 43.3 months (95% CI 21.6–not estimable [NE]) at a median follow-up of 32.3 months. Median progression-free survival was 35.5 months (95% CI 23.4–NE) at a median follow-up of 34.0 months. Median overall survival (OS) was not reached (NR; 95% CI 48.7–NE) at a median follow-up of 46.4 months; the 48-month OS rate was 71% (95% CI 54–88). Median OS was NR (95% CI 48.7–NE) in DTC and 8.8 months (95% CI 2.6–NE) in ATC. At data cut-off, five pts who had disease progression continued treatment for ≥4 weeks due to continued clinical benefit. Treatment-related adverse events (TRAEs) were predominantly Grade 1–2. Grade ≥3 TRAEs were reported in two (7%) pts (anemia and decreased lymphocyte count). There were no treatment discontinuations due to TRAEs. Conclusions: Laro continues to demonstrate a rapid and durable response, extended survival, and a favorable safety profile in pts with TRK fusion DTC. Limited single-agent activity was observed in ATC. These results support the wider adoption of next generation sequencing panels, which include NTRK gene fusions, in pts with advanced TC prior to the initiation of any systemic therapy. Clinical trial information: NCT02576431 , NCT02122913 , NCT02637687 .