Abstract 469: Comprehensive, large scale analysis of ALK, ROS1, RET, NTRK1 and NRG1 transcripts in lung cancer reveals over-expressing, potentially targetable patients
Authors: Aguado Cristina , Teixido Cristina , Capitan Ana Gimenez , Marin Elba , Roman Ruth , Rodriguez Sonia , Moya Irene , Reyes Roxana , Viñolas Nuria , Viteri Santiago , Aguilar Andres , Rosell Rafael , Reguart Noemi , Molina-Vila Miguel Angel 
Published: July 2021

Abstract
Background: Fusion involving anaplastic lymphoma kinase (ALK), RET proto-oncogene (RET) or ROSproto-oncogene 1, receptor tyrosine kinase (ROS1), neurotrophic receptor tyrosine kinase 1 (NTRK1)and neuregulin 1 (NRG1) are present in lung cancer (LC) and represent important biomarkers fortargeted therapies. However, little is known about the RNA expression levels of some of these genesregardless of fusions.
Methods: We used a custom nCounter panel (NanoString Technologies) designed to detect fusionsand mRNA expression levels of ALK, ROS1, RET, NTRK1 and NRG1 in formalin-fixed paraffin embedded(FFPE) samples. RNA was purified from lung cancer tumor samples and analyzed with the panel. Thecounts corresponding to the 3' probes were normalized using the geometrical mean of thehousekeeping genes and then added to evaluate total mRNA expression levels. Cut-off values for veryhigh expression levels were established as the average counts in all samples (s.) studied for each geneplus three times the standard deviation.
Results: A total of 580 LC s. from two different institutions were retrospectively analyzed for ALK,ROS1, RET and NTRK1 mRNA levels. Very high levels of ALK mRNA were found in 76 s. (13%). Of them,69/76 were also positive for EML4-ALK fusions and 61/76 had adenocarcinoma histology (ADC). OneALK-translocated patient with a sample with low levels of ALK mRNA did not respond to therapy.Twenty-two s. (3.8%) showed very high levels of ROS1 mRNA and 17/22 were ADC. In contrast withALK, only 4/22 had a concomitant ROS1 fusion. Among the remaining 16 s. with very high levels ofROS1 mRNA, 11 were ALK or EGFR positive and two were wt for the more common lung ADC geneticalteration. Regarding RET, very high expression levels were found in 11 s. (2%), only one of themshowed a RET fusion. Among the remaining 10 s., 6 presented neuroendocrine features and only 2were ADC. Regarding NTRK1, 4 s. showed very high expression levels of mRNA and only one of themwas positive for NTRK1 translocation. Finally, 116 LC s were analyzed for NRG1; very high mRNA levelswere detected in 2 cases, none of them translocated.
Conclusions: Very high expression of ALK mRNA in NSCLC is associated with EML4-ALK translocations.In contrast, a significant number of fusion negative patients show high ROS1, RET and NTRK1 mRNAvery high levels. Further research is warranted to determine the clinical relevance of this finding.
Citation Format: Cristina Aguado, Cristina Teixido, Ana Gimenez Capitan, Elba Marin, Ruth Roman, Sonia Rodriguez, Irene Moya, Roxana Reyes, Nuria Viñolas, Santiago Viteri, Andres Aguilar, Rafael Rosell, Noemi Reguart, Miguel Angel Molina-Vila. Comprehensive, large scale analysis of ALK, ROS1, RET, NTRK1 and NRG1 transcripts in lung cancer reveals over-expressing, potentially targetable patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 469.