NTRK Fusion Landscape in 195 Positive Cases of 17 Tumors: A Chinese Multicenter Retrospective Study with Optimized Pan-TRK IHC Screening.

Neurotrophic tyrosine receptor kinase (NTRK) fusions are crucial in tumorigenesis and in guiding targeted therapy with TRK inhibitors. However, their rarity, fusion heterogeneity, and limitations of conventional pan-TRK immunohistochemistry (IHC) impede accurate clinical detection. This multicenter retrospective study analyzed 374 NGS/FISH-validated samples (195 NTRK - positive and 179 NTRK - negative) collected from 12 Chinese centers to investigate fusion heterogeneity and refine the interpretation of pan-TRK IHC. We developed an amplified protocol by combining the traditional pan-TRK IHC (EPR17341) with the OptiView Amplification kit and established new interpretation criteria. A total of 40 solid tumor types were included, and 23 unique fusion partners were identified. Papillary thyroid cancer was the most common NTRK-positive tumor (49.74 %) and harbored all three NTRK subtypes. Among NTRK-positive samples, NTRK3 (74.87 %) was the most prevalent subtype, followed by NTRK1 (23.59 %). ETS variant transcription factor 6 (ETV6) was the most frequent fusion partner, identified in 122 out of 195 cases. It was uniquely shared across all three NTRK subtypes, with its fusion to NTRK1 being reported for the first time. NTRK1 and NTRK3 exhibited marked fusion partner specificity, with no overlap in their associated partners except for ETV6. The optimized pan-TRK IHC protocol significantly improved staining efficiency by enhancing intensity and clarity. Consequently, the newly established criteria (cytoplasmic intensity ≥1 in ≥50% of tumor cells or any nuclear intensity ≥1) exhibited outstanding detection performance, achieving an overall sensitivity of 94.36% and increasing specificity to 79.89%, compared to 60.22% under the conventional one. Particularly, the detection sensitivity for NTRK3 fusions was significantly enhanced and reached 95.89 %. This study contributes to clarifying NTRK fusion distribution in patients and validates a standardized, sensitive pan-TRK IHC strategy for clinical screening.