Immunohistochemistry and Next-Generation Sequencing for NTRK Fusion detection in Differentiated Thyroid Cancer of Children, Adolescents and Young Adults

Abstract

Abstract Introduction: Pan-Trk immunohistochemistry (IHC) staining can assess the protein expression from NTRK gene fusions a- Little is known about its utility in differentiated thyroid cancer (DTC) samples from children, adolescents, and young adults (CAYA) patients. Objective: Investigate Pan-Trk IHC sensitivity and specificity in DTC samples from CAYA patients. Methods:Tumor samples obtained from 79 CAYA patients (age <21years) diagnosed with DTC between January 2010 and January 2021 were retrospectively recruited from four health centers from state of Bahia e Paraíba, Brazil. NTRK gene fusion testing of all archival FFPE tumor samples: Pan-TRK IHC staining for TRKA, TRKB and TRKC protein expression were performed and then analyzed with RNA-based next-generation sequencing (NGS) assay in order to confirm IHC pan-TRK result and elucidate fusion partner. Results:Pan-Trk IHC: 3 of 79 cases had positive pan-Trk expression: NGS sequencing: 04- were identified with NTRK gene fusion, Pan-Trk IHC was negative in all 4 NTRK NGS-positive cases. 25 of 79 NTRK NGS-negative control cases had concordant negative pan-TRK IHC results. Therefore, our rate of false positive pan-Trk IHC results was 3/25 (12%). The overall results for pan-Trk IHC in our cohort of NGS-negative cases was: (i) sensitivity (0%), (ii) specificity (96%), (iii) positive predictive value (94.7%), (iv) negative predictive value (91%). Conclusions: Pan-Trk IHC was not a tissue-efficient screen for NTRK fusions in DTC from CAYA patients. This is the largest cohort of CAYA DTC cases stained with pan-Trk IHC, and it is the first to detail the sensitivity and specificity of pan-Trk IHC regarding the data obtained by targeted RNA-based NGS panel in DTC.