BackgroundThe South West Thames Centre for Genomics implemented a wider diagnostic Next Generation Sequencing (NGS) gene panel for eligible cancer patients undergoing diagnostic testing whilst restricting data analysis and reporting for BRCA1/BRCA2/PALB2/CHEK2 1100delC only as per contemporaneous guidelines. This study investigated the cost-utility of reanalyzing existing diagnostic grade extended panel data for truncating germline pathogenic variants (GPVs) in known moderate risk cancer susceptibility genes (CSGs) and performing follow-up genetic testing for first-degree relatives if patients have an identified CSG allele. MethodsReanalysis of existing NGS data was undertaken in 889 samples from cancer patients contemporaneously eligible through the NHS England National Genomic Test Directory (NGTD) codes R207 (ovarian) or R208 (breast) who had tested negative for BRCA1/BRCA2/PALB2 and CHEK2 1100delC founder variant. We modeled the cost and health outcomes for comparisons between: 1. Extending reanalysis to ATM truncating GPVs (partial extended testing) versus historical genetic testing, and 2. Extending analysis to ATM truncating GPV/BRIP1 truncating GPV/CHEK2 truncating GPV excluding CHEK2 1100delC/RAD51C truncating GPV/RAD51D truncating GPV (full extended testing) versus historical genetic testing. ResultsFor partial extended testing, the ICER compared with historical genetic testing was UK£49,671/QALY. For full extended testing, the ICER compared with historical genetic testing of historical genetic testing was UK£5716/QALY. The full extended testing remained cost-effective with a 30% increase in genetic testing cost. ConclusionWhere existing NGS data for cancer susceptibility genes is stored to diagnostic standard in UK laboratories, this study suggests it is cost-effective to analyze, report and clinically manage patients and relatives by extended analysis to an 8-gene panel compared to the historical genetic testing.