Loxo Oncology, Inc. announced an updated clinical trial data of an anti-cancer drug, larotrectinib, at the American Association for Cancer Research (AACR) Special Conference on Pediatric Cancer Research. TRK is a protein that is related to cell growth and survival signaling pathways. Fusion genes of TRK leads to constitutively activated growth signaling and tumor development. Larotrectinib is a TRK inhibitor currently under development for cancer treatment. In the phase I pediatric clinical trial (SCOUT), 24 patients with pediatric cancer were enrolled. 17 patients with TRK fusion cancers were diagnosed with infantile fibrosarcoma, thyroid cancer, and various soft tissue sarcomas. Among 17 patients with TRK fusion cancers, the overall response rate (ORR) was 93%, including 13% had complete responses (CR) and 80% had partial responses (PR). At the July 17, 2017, the data cutoff date, 94% of patients with TRK fusion cancers continued to receive drug treatment or had received surgery with curative intent. The most common treatment-related adverse events were grade 1 at the Phase 2 dose, including increased liver function tests, neutropenia, and nausea. These results showed the efficiency of larotrectinib in pediatric cancer with TRK fusion.