P1.02-025 Evaluation of NGS and RT-PCR Methods for ALK Assessment in European NSCLC Patients: Results from the ETOP Lungscape Project

Abstract

The reported prevalence of ALK rearrangement in NSCLC ranges from 2%-7%, depending on population and detection method. The primary standard diagnostic method is fluorescence in situ hybridization (FISH). Recently, immunohistochemistry (IHC) has also proven to be a reproducible and sensitive technique. Reverse transcriptase-polymerase chain reaction (RT-PCR) has been advocated and most recently the advent of targeted Next-Generation Sequencing (NGS) for ALK and other fusions has become possible. This is one of the first studies comparing all 4 techniques in resected NSCLC from the large ETOP Lungscape cohort. 96 cases from the ETOP Lungscape iBiobank (N=2709) selected based on any degree of IHC staining (clone 5A4 antibody, Novocastra, UK) were examined by FISH (Abbott Molecular, Inc.; Blackhall, JCO 2014), central RT-PCR and NGS. H-score 120 is used as cutoff for IHC+. For both RT-PCR and NGS, RNA was extracted from the same formalin-fixed, paraffin-embedded tissues. For RT-PCR, primers were used covering the most frequent ALK translocations. For NGS, the Oncomine™ Solid Tumour Fusion Transcript Kit was used, allowing simultaneous sequencing of 70 ALK, RET and ROS1 specific fusion transcripts associated with NSCLC, as well as novel ALK translocations using 5’-3’ ALK gene expression ‘Imbalance Assay’. NGS provided results for 90 cases, while RT-PCR for 77. Overall, 70 cases have results for all 4 methods, with fully concordant 60 (85.7%) cases (49 ALK-, 11 ALK+). Before employing the ‘Imbalance Assay', in 5 of the remaining 10 cases, NGS differs from the other methods (3 NGS-, 2 NGS+), while in the other 5, NGS agrees with RT-PCR in all, IHC in 2, and FISH in 1. Using the concordant result of at least two of the three methods as true negative/positive, the specificity and sensitivity of the fourth is 96/94/100/96% and 94/94/89/72% for IHC/FISH/RT-PCR/NGS, respectively (incorporating imbalance: NGS sensitivity=83%). Imbalance scores are presented here for 18 NGS- cases: 9 ‘NGS-/FISH+/IHC+’, 9 ‘NGS-/FISH-/IHC-‘. Among the ‘NGS-/FISH+/IHC+’, there is strong evidence of imbalance in 4 cases (score’s range: 0.0144-0.0555), uncertain in 5 (range: 0.0030-0.0087), and no evidence (scores≤0.0004) in the 9 negative cases. NGS is a useful screening tool for ALK rearrangement status, superior to RT-PCR when RNA yield is limited. When using NGS, it is critically important to integrate the 5’-3’ imbalance assay and to confirm with one or more additional methods in the ‘imbalance’ cases. Data further highlight the possibility of missing actionable rearrangements when only one screening methodology is available.