Immunohistochemical Evaluation of Pan-TRK Expression

FFPE TMA blocks were cut in 4 µm-thick sections and placed on slides. IHC staining for pan-TRK expression was performed on the Benchmark Ultra platform (Ventana Medical Systems, Tucson, AZ) with iVIEW DAB Detection Kit (Ventana Medical Systems, Tucson, AZ), using a commercially available pan-TRK assay (rabbit monoclonal antibody, clone EPR17341, Assay, RTU, Roche, Ventana). Normal appendix and brain tissues were used as positive controls. The immunohistochemical evaluation included (i) location (membranous, cytoplasmic, nuclear, mixed), (ii) intensity (strong, moderate, weak, and negative) and (iii) the extent (percentage of positive tumor cells) of the IHC staining. Membranous, cytoplasmic, and nuclear staining patterns were considered positive if ≥1% of tumor cells exhibited positivity at any intensity above background [29 (link)]. Diffuse staining was defined as moderate to strong expression in ≥50% of tumor cells [39 (link)].