Abstract IA15: Tissue-agnostic development of TRK inhibitors for pediatric cancer

Abstract

Abstract Fusions involving in the NTRK1, NTRK2, and NTRK3 genes that encode the TRKA, TRKB, and TRKC neurotrophin receptors (TRK fusions) occur across a wide range of cancers in children and adults. These fusions result in constitutive expression and ligand-independent activation of the TRK kinase. TRK fusions are pathognomonic for certain rare cancers, including infantile fibrosarcoma and cellular congenital mesoblastic nephroma, and occur at a lower frequency across a range of more common cancers in children including soft-tissue sarcomas, gliomas, and leukemias. Recently, larotrectinib was FDA approved for the treatment of TRK fusion solid tumors in children and adults, representing the first kinase inhibitor to receive FDA histology-agnostic approval for the treatment of cancer. This approval was based on a combined analysis of three clinical trials, including an ongoing pediatric phase 1/2 trial that demonstrated a 94% response rate in 34 children with TRK fusion-positive solid tumors. Remarkably, due to nearly concurrent development in pediatrics and adults, more than 30% of the patients with TRK fusion solid tumors treated with larotrectinib on clinical trials to date have been children. Other TRK inhibitors are also in pediatric development, including entrectinib and LOXO-195, and clinical trials of additional agents including repotrectinib are planned. Entrectinib, which also antagonizes ROS1 and ALK, was reported to induce responses in 11/11 children whose tumors harbored fusions of the TRK, ROS1 or ALK genes. LOXO-195 and repotrectinib have the potential to antagonize resistance mutations that can develop during treatment with first-generation TRK inhibitors, and we reported a 45% response rate to LOXO-195 among 20 patients enrolled to either single-patient treatment protocols or an ongoing pediatric and adult phase 1 study who harbored a TRK kinase resistance mutation. In this talk, I will review the data on the use of TRK inhibitors for TRK fusion cancers in children, discuss unanswered questions related to the use of TRK inhibitors in children and planned clinical trials designed to address these, and highlight the challenges and opportunities that arise when studying novel therapies for rare, molecularly defined diseases. Citation Format: Theodore W. Laetsch. Tissue-agnostic development of TRK inhibitors for pediatric cancer [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr IA15.