Randomised clinical trials (RCTs) are gold standard in evidence-based medicine, but follow-up typically relies on clinic visits and trial-specific data collection. Much of this information overlaps with routinely collected healthcare systems data (HSD), such as electronic health records and national registries. Leveraging HSD for trial follow-up has the potential to reduce cost, time and resource burden. However, concerns remain about data quality and evidence is needed to show that HSD-based outcomes are reported to an equivalent standard to trial-specific data.The Blood Cancer Clinical Trials Long-term Follow-up Using Integrated Healthcare Systems platform will link data collected from multiple myeloma clinical trials with HSD to create a research database supporting extended follow-up and further methodological and clinical research.