Feasibility of two-step approach for screening NTRK fusion in two major subtypes of non-small cell lung cancer within a large cohort

Our objective is to investigate a cost-effective approach to screen for NTRK fusion in the major subtypes of non-small cell lung cancer (NSCLC). Evaluate the concordance between immunohistochemistry (IHC) and next-generation sequencing (NGS), as well as between fluorescence in situ hybridization (FISH) and NGS, to detect any discrepancies in methodological consistency between lung adenocarcinoma (LADC) and lung squamous cell carcinoma (LSCC). Analyze the factors influencing IHC results. A cohort of 1654 patients with NSCLC underwent screening for NTRK fusion using whole slide IHC. The positive cases were analyzed by both FISH and NGS. Totally, 57 tested positive for pan-TRK, with positivity rates of 0.68% (10/1467) for LADC and 29.01% (47/162) for LSCC. FISH showed separate NTRK1 and NTRK3 rearrangements in two pan-TRK-positive LADCs, while all LSCCs tested negative. NGS confirmed functional NTRK fusion in two FISH-positive cases: one involving TPM3-NTRK1 and the other involving SQSTM1-NTRK3. A non-functional fusion of NTRK2-XRCC1 was detected in LSCC, while FISH was negative. According to our approach, the prevalence of NTRK fusion in NSCLC is 0.12%. The concordance rate between IHC and RNA-based NGS was 20% (2/10) in LADC and 0% (0/162) in LSCC. When the positive criteria increased over 50% of tumor cells showing strong staining, the concordance would be 100% (2/2). A concordance rate of 100% (2/2) was observed between FISH and RNA-based NGS in LADC. The expression of pan-TRK was significantly correlated with the tumor proportion score (TPS) of PD-L1 (p < 0.05) and transcript per million (TPM) values of NTRK2 (p < 0.05). We recommend using IHC with strict criteria to screen NTRK fusion in LADC rather than LSCC, confirmed by RNA-based NGS directly. When the NGS results are inconclusive, FISH validation is necessary.