Immunohistochemistry and next-generation sequencing for NTRK fusion detection in differentiated thyroid cancer of children, adolescents and young adults

Introduction: Pan-TRK immunohistochemistry staining can assess the protein expression from NTRK gene fusions. A little is known about its utility in differentiated thyroid cancer samples from children, adolescents, and young adults patients. Objective: Investigate pan-TRK immunohistochemistry sensitivity and specificity in differentiated thyroid cancer samples from children, adolescents, and young adults patients. Methods: Tumor samples obtained from 79 children, adolescents, and young adults patients (age <21 years) diagnosed with differentiated thyroid cancer 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 immunohistochemistry staining for TRKA, TRKB and TRKC protein expression were performed and then analyzed with RNA-based next-generation sequencing assay to confirm immunohistochemistry pan-TRK result and elucidate fusion partner. Results: Pan-TRK immunohistochemistry: 3 of 79 cases had positive pan-TRK expression: next-generation sequencing; 4 were identified with NTRK gene fusion, pan-TRK immunohistochemistry was negative in all 4 NTRK next-generation sequencing-positive cases. 25 of 79 NTRK next-generation sequencing-negative control cases had concordant negative pan-TRK immunohistochemistry results. Therefore, our rate of false positive pan-TRK immunohistochemistry results was 3/25 (12%). The overall results for pan-TRK immunohistochemistry in our cohort of next-generation sequencing-negative cases was: (i) sensitivity (0%), (ii) specificity (96%), (iii) positive predictive value (94.7%), (iv) negative predictive value (91%). Conclusion: Pan-TRK immunohistochemistry was not a tissue-efficient screen for NTRK fusions in differentiated thyroid cancer from children, adolescents, and young adults patients. This is the largest cohort of from children, adolescents, and young adults differentiated thyroid cancer cases stained with pan-TRK immunohistochemistry, and it is the first to detail the sensitivity and specificity of pan-TRK immunohistochemistry regarding the data obtained by targeted RNA-based next-generation sequencing panel in differentiated thyroid cancer.