56 New research shows that RNA-based testing can significantly improve detection of MET exon 14 skipping, a critical biomarker used to determine eligibility for targeted lung cancer therapies. The mutations that cause this skipping occur in 3%–4% of Non-Small Cell Lung Cancer (NSCLC) patients. They are exceptionally heterogeneous and span a broad splice-site region, making them difficult to capture reliably with either DNA- or RNA-based sequencing assays. The study, published in The Journal of Molecular Diagnostics by Elsevier, analysed a large real-world cohort alongside multinational external quality assessment schemes, aiming to improve assay design, variant interpretation, and diagnostic workflows in molecular pathology laboratories. Researchers systematically characterised the alterations seen in routine clinical practice, assessed their functional consequences at the RNA level, identified diagnostic pitfalls, and evaluated laboratory performance. The research revealed the extraordinary diversity of genomic alterations capable of causing MET exon 14 skipping, identifying 171 distinct mutations affecting the splice region. Of 379 NSCLC samples analysed with mutations in MET exon 14 and adjacent splice sites, 114 were tested using both DNA- and RNA-based sequencing. RNA analysis confirmed exon 14 skipping in more than 100 different alteration types and showed that some clinically relevant events, including large genomic deletions and a synonymous variant affecting splicing, can be missed or misinterpreted by DNA testing alone. “Although MET exon 14 is a well-established predictive biomarker, our findings highlight a level of molecular complexity that is often underappreciated in routine diagnostic practice,” said lead investigator Carina Heydt, PhD, of the University of Cologne. The external quality assessment schemes, which used both tissue- and liquid-biopsy samples, found excellent laboratory performance for tissue-based testing, with an overall success rate of 98%, indicating that reliable detection is achievable across laboratories using properly validated methods. Liquid biopsy testing proved far more challenging. Performance improved from a 37.5% success rate in the first assessment round in 2022 to 63% in the second round in 2024, though detecting MET exon 14 alterations in circulating tumour DNA remains technically demanding. Accurate detection of MET exon 14 skipping determines patient eligibility for MET-targeted therapies such as capmatinib and tepotinib, which have shown efficacy in eligible patients. The skipping event removes a regulatory domain, leading to prolonged MET signalling that drives tumour growth in a subset of lung cancers, particularly among older patients and those with specific histologies. “To improve diagnostic accuracy, incorporating RNA-based confirmation, where feasible, can improve sensitivity and specificity for identifying true exon-skipping events,” Dr Heydt said. “This research has important implications for routine clinical molecular pathology. Our study provides evidence supporting the complementary role of RNA-based testing in the assessment of MET exon 14 alterations and highlights the value of external quality assessment programmes in monitoring assay performance, identifying analytical limitations, promoting harmonisation of testing strategies, and ensuring accurate and reproducible results for patient selection for MET-targeted therapies.” Experts say tissue-based testing remains robust, but ongoing improvements in liquid-biopsy technology are needed to broaden access for patients where tissue sampling is difficult. The findings support wider efforts in precision oncology to refine biomarker testing for NSCLC, where accurate genomic profiling directly shapes treatment decisions and patient outcomes. Laboratories are encouraged to validate comprehensive assays that integrate both DNA and RNA analysis where possible, alongside continued participation in quality assurance schemes to maintain high standards.