Abstract CT228: Concordance between tissue and circulating tumor DNA (ctDNA) testing for neurotrophic tyrosine receptor kinase (NTRK) gene fusions in larotrectinib (laro) clinical trials
Authors: Rudzinski Erin R. , Ladanyi Marc , Ritterhouse Lauren L. , Sahm Felix , Norenberg Ricarda , Zheng Hong , Chen Chi , Bernard-Gauthier Vadim , Brega Nicoletta , van Tilburg Cornelis M. , Lin Jessica J. , Brose Marcia S. , Lassen Ulrik N. , McDermott Ray , Laetsch Theodore W. , Hong David S. , Drilon Alexander , Roy-Chowdhuri Sinchita 
Published: April 2023

Abstract
Background: NTRK gene fusions are oncogenic drivers in various tumor types. Laro, a highly selective and central nervous system (CNS)-active tropomyosin receptor kinase (TRK) inhibitor, is approved for the treatment of patients (pts) with TRK fusion cancer. Laro demonstrated an objective response rate (ORR) of 69% in 244 pts with solid (non-primary CNS) tumors (Drilon et al. ASCO 2022). Here, we report on the concordance between baseline local tissue-based testing with central tissue-based and liquid biopsy-based ctDNA testing to identify NTRK gene fusions.
Methods: Pts with non-primary CNS TRK fusion cancer who underwent independent review committee assessments by July 15, 2019, in three laro clinical trials (NCT02122913, NCT02576431, and NCT02637687) were included. Tumor NTRK gene fusion status was determined locally by a variety of methods, and centrally by next-generation sequencing in both tissue (using Illumina TruSight™ Oncology Comprehensive) and ctDNA (using Guardant360® or GuardantOMNI®) at baseline. Data cut-off: July 20, 2021.
Results: Of the 164 pts with NTRK fusions identified by local testing, 117 had evaluable tissue samples for central testing, and 99 had evaluable liquid biopsy samples. In total, 81.2% (95/117) of tumors had the fusion confirmed by central tissue testing. ctDNA testing detected NTRK gene fusions in 33.3% (33/99) of patients. Positive predictive values for each NTRK gene fusion are shown in the Table. The ORR for pts with NTRK gene fusions determined by local and central testing will be presented.
Conclusions: A high proportion of tumors with locally identified NTRK gene fusions were confirmed centrally. At present, analysis of ctDNA is significantly less sensitive at detecting NTRK gene fusions. A negative ctDNA result requires next-generation sequencing testing of a tissue biopsy. Further research is needed to improve the sensitivity of ctDNA gene fusion detection.
Table NTRK gene fusion Tissue-based LT Tissue-based CT ctDNA-based CT with LB Fusion confirmed, n Fusion confirmed, n Fusion not detected, n Unavailable samples, n† PPV‡: CT vs tissue-based LT, % Fusion confirmed, n Fusion not detected, n Unavailable samples, n† PPV‡: LB vs tissue-based LT, % NTRK1 68 35 14 19 71.4 20 34 14 37.0 NTRK2 4 3 1 0 75.0 0 4 0 0 NTRK3 92§ 57 7 28 89.1 13 28 51 31.7 †Includes no sample available and sample QC failed. ‡Calculated as a percentage of the number of confirmed fusions over the number of available samples. §Includes 9 inferred NTRK3 fusions. CT, central testing; ctDNA, circulating tumor DNA; LB, liquid biopsy; LT, local testing; NTRK, neurotrophic tyrosine receptor kinase; PPV, positive predictive value; QC, quality control.
Citation Format: Erin R. Rudzinski, Marc Ladanyi, Lauren L. Ritterhouse, Felix Sahm, Ricarda Norenberg, Hong Zheng, Chi Chen, Vadim Bernard-Gauthier, Nicoletta Brega, Cornelis M. van Tilburg, Jessica J. Lin, Marcia S. Brose, Ulrik N. Lassen, Ray McDermott, Theodore W. Laetsch, David S. Hong, Alexander Drilon, Sinchita Roy-Chowdhuri. Concordance between tissue and circulating tumor DNA (ctDNA) testing for neurotrophic tyrosine receptor kinase (NTRK) gene fusions in larotrectinib (laro) clinical trials [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT228.