Detection of Fusions and TRK Expression and Performance of pan-TRK Immunohistochemistry in Routine Diagnostics: Results from a Nationwide Community-Based Cohort.

Gene fusions involving , and are rare drivers of cancer that can be targeted with histology-agnostic inhibitors. This study aimed to determine the nationwide landscape of /TRK testing in the Netherlands and the usage of pan-TRK immunohistochemistry (IHC) as a preselection tool to detect NTRK fusions. All pathology reports in 2017-2020 containing the search term 'TRK' were retrieved from the Dutch Pathology Registry (PALGA). Patient characteristics, tumor histology, /TRK testing methods, and reported results were extracted. /TRK testing was reported for 7457 tumors. Absolute testing rates increased from 815 (2017) to 3380 (2020). Tumors were tested with DNA/RNA-based molecular assay(s) (48%), IHC (47%), or in combination (5%). A total of 69 fusions involving ( = 22), ( = 6) and ( = 41) were identified in tumors from adult ( = 51) and pediatric ( = 18) patients. In patients tested with both IHC and a molecular assay ( = 327, of which 29 fusion-positive), pan-TRK IHC had a sensitivity of 77% (95% confidence interval (CI), 56-91) and a specificity of 84% (95% CI, 78-88%). These results showed that pan-TRK IHC has a low sensitivity in current routine practice and warrants the introduction of quality guidelines regarding the implementation and interpretation of pan-TRK IHC.