Aims
NTRK-rearranged tumours are rare but can be successfully treated using anti-TRK–targeted therapies making NTRK testing important for treatment choices in patients with advanced cancers. Pan-Trk immunohistochemistry (IHC) has become a valuable and affordable screening tool in many laboratories. Unfortunately, the choice of antibodies and IHC protocols to investigate biomarkers is not standardized. In this study, we compared the performance of four pan-Trk IHC methods, using three different clones, primarily in NTRK- fusion positive tumours.
Method
We studied the performance of four pan-Trk IHC methods, using three different clones: EPR17341 (Abcam and Ventana), EP1058Y (Abcam), A7H6R (Cell Signaling) in 22 molecularly confirmed NTRK-rearranged tumours. Additionally, selected NTRK-fusion negative tumours were further included: NTRK mutated (n=8) and amplified (N=15) tumours as well as NTRK-fusion negative tumours driven by other gene fusions such as ALK, ROS1 and BCOR (n=20) as well as salivary gland tumours (n=16). Interrater agreement of three pathologist was additionally calculated, including H-score.
Result
With clone EPR17341 (Abcam in house and ready to use Ventana protocol) all molecularly confirmed NTRK 1-3 rearranged tumours were positively detected by immunohistochemistry, while the other clones missed NTRK2-3-rearranged tumours. For the fusion negative cohort we found the best performance (least false positive cases) using the clone A7H6R (Cell Signalling).
Conclusion
Given the therapeutic importance, testing for NTRK rearrangements in daily practice has become necessary and despite IHC being a fast and affordable tool, using it in routine diagnostics is complicated and requires a high level of expertise.
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