RT Journal Article SR Electronic T1 FOCUS4 biomarker laboratories: from the benefits to the practical and logistical issues faced during 6 years of centralised testing JF Journal of Clinical Pathology JO J Clin Pathol FD BMJ Publishing Group Ltd and Association of Clinical Pathologists SP jclinpath-2022-208233 DO 10.1136/jclinpath-2022-208233 A1 Susan D Richman A1 Gemma Hemmings A1 Helen Roberts A1 Niall Gallop A1 Rachel Dodds A1 Lyndsay Wilkinson A1 Jonathan Davis A1 Rhian White A1 Emma Yates A1 Bharat Jasani A1 Louise Brown A1 Tim S Maughan A1 Rachel Butler A1 Philip Quirke A1 Richard Adams YR 2022 UL http://jcp.bmj.com/content/early/2022/03/06/jclinpath-2022-208233.abstract AB Aims FOCUS4 was a phase II/III umbrella trial, recruiting patients with advanced or metastatic colorectal cancer, between 2014 and 2020. Molecular profiling of patients’ formalin-fixed, paraffin-embedded tumour blocks was undertaken at two centralised biomarker laboratories (Leeds and Cardiff), and the results fed directly to the Medical Research Council Clinical Trials Unit, and used for subsequent randomisation. Here the laboratories discuss their experiences.Methods Following successful tumour content assessment, blocks were sectioned for DNA extraction and immunohistochemistry (IHC). Pyrosequencing was initially used to determine tumour mutation status (KRAS, NRAS, BRAF and PIK3CA), then from 2018 onwards, next-generation sequencing was employed to allow the inclusion of TP53. Protein expression of MLH1, MSH2, MSH6, PMS2 and pTEN was determined by IHC. An interlaboratory comparison programme was initiated, allowing sample exchanges, to ensure continued assay robustness.Results 1291 tumour samples were successfully analysed. Assay failure rates were very low; 1.9%–3.3% for DNA sequencing and 0.9%–1.3% for IHC. Concordance rates of >98% were seen for the interlaboratory comparisons, where a result was obtained by both laboratories.Conclusions Practical and logistical problems were identified, including poor sample quality and difficulties with sample anonymisation. The often last-minute receipt of a sample for testing and a lack of integration with National Health Service mutation analysis services were challenging. The laboratories benefitted from both pretrial validations and interlaboratory comparisons, resulting in robust assay development and provided confidence during the implementation of new sequencing technologies. We conclude that our centralised approach to biomarker testing in FOCUS4 was effective and successful.Data are available on reasonable request. The sequencing data analysed during this study are available from the corresponding author on reasonable request.