Elfving H, Broström E, Moens LNJ, et al. - This study was undertaken to investigate the newly introduced diagnostic immunohistochemical assay (clone EPR17341) on a representative non-small cell lung cancers (NSCLC) cohort. In this study, cancer tissue from 688 clinically and molecularly extensively annotated NSCLC individuals were comprised on tissue microarrays and stained with the pan-TRK antibody clone EPR17341. Researchers further examined the positive cases with the TruSight Tumor 170 RNA assay (Illumina). They also investigated selected cases with a NanoString neurotrophic tropomyosin receptor kinase (NTRK) fusion assay. NTRK RNA expression data were available from previous RNA sequencing analysis for 199 cases. In non-small cell lung cancer, the presence of NTRK fusion genes is very rare. The findings demonstrate that the use of the immunohistochemical NTRK assay will yield a small number of false-positive cases. According to the findings, this should be considered when the assay is applied as a screening tool in clinical diagnostics.