[Comparison of the methods for detecting NTRK gene fusion variations in papillary thyroid carcinoma]

Objective: To investigate the frequency of neurotrophic tyrosine receptor kinase (NTRK) gene variations in papillary thyroid carcinoma (PTC) and to analyze the feasibility of detecting tropomyosin receptor kinase (TRK) proteins using immunohistochemistry (IHC) to predict the fusion variation of NTRK. Methods: A cohort of 848 PTC cases was collected at the Department of Pathology, Shenzhen People's Hospital from June 2017 to June 2020. The expression levels of TRK proteins were detected using IHC in 848 PTC samples, and the DNA-based next generation sequencing (NGS) was performed to detect NTRK rearrangements in 150 PTCs. Results: There were 242 males and 606 females, with an age range of 9-83 years. In 120 cases with TRK expression detected by IHC, 13 cases were confirmed to harbor a NTRK gene fusion by NGS. The frequency of NTRK fusion in PTC was 1.5% (13/848). The sensitivity and specificity of TRK-IHC positivity for screening NTRK fusion in PTC were 100% and 21.9%, respectively. The specificity of weak-, moderate- and strong-positive stains of TRK IHC were 23.8%, 76.9% and 93.8%, respectively. The specificity of NTRK gene fusion was predicted to increase with the enhanced intensity of IHC staining. In BRAF V600E negative PTC samples, the specificity of weak-and moderate-positive stains of TRK IHC increased to 62.5% and 96.8%, respectively. Seven NTRK fusion partners were found in the PTC, including EML4, ETV6, CDH1, GJD2, TPR, TFG and SQSTM1. Conclusions: There is a low variation frequency of NTRK gene fusion in PTC. TRK IHC can be used as a screening method for NTRK fusion variation in PTC. The specificity of TRK IHC predicting NTRK fusion can be further enhanced by increasing the cutoff value of the positive cell number and staining intensity of TRK-IHC staining, or being combined with BRAF V600E negativity.