A Pediatric Phase I Study Of Larotrectinib, A Highly Selective Inhibitor Of The Tropomyosin Receptor Kinase (Irk) Family.

10510Background: Larotrectinib is the first selective small-molecule inhibitor of TRKA, B, and C in clinical development. Data from the adult phase I trial demonstrate prolonged responses in patients (pts) with TRK fusions and a favorable tolerability profile. Methods: This multicenter, rolling 6 phase I study enrolled pts with refractory solid or CNS tumors aged ≥ 1 month – 21 years. Pts were dosed orally BID on a continuous 28-day schedule either by capsule or solution. Pharmacokinetic (PK)-directed intra-subject dose escalation was permitted, with exposures targeting the adult recommended Phase II dose (RP2D) of 100 mg BID. The primary objective was to define the MTD / RP2D; secondary objectives included PK and efficacy using RECIST v1.1. Results: As of December 31, 2016, 17 pts (12 with TRK fusions, 5 without TRK fusions) with a median age of 5.2 years (0.4 – 18.3) were enrolled to 3 dose levels. Pts were enrolled with fusions of all 3 NTRK genes: NTRK1 (n=6), NTRK2 (n=1), and NTRK3 (n=5) in heterogen...