{"entity":{"id":"external-control-arm","kind":"term","name":"External and synthetic control arms","aka":["external control","external control arm","external comparator","synthetic control","synthetic control arm","historical control","historical controls","historical comparison","real-world comparator","real-world control","natural history control","matched cohort","propensity-matched","propensity score","Bayesian borrowing","dynamic borrowing","hybrid control","external control arms","external controls","synthetic controls"],"tldr":"Instead of randomising patients to a control group, comparing a single-arm trial against patients treated in the past or recorded in registries, matched by propensity scores. Regulators accepted this for eflornithine in neuroblastoma and other rare cancers, but unmeasured differences between the groups, including changes in supportive care between eras, can masquerade as drug effects.","summary":"External controls draw on prior trials, electronic health records or registries (Flatiron, TriNetX) and use propensity matching or Bayesian dynamic borrowing to align populations; regulators have accepted them for eflornithine in neuroblastoma, several paediatric and rare-cancer approvals, and in the EU for some CAR-T comparisons. Weaknesses are unmeasured confounding, different eras of supportive care ('bias when standard of care changes between eras'), and differences in outcome assessment. FDA guidance (2023) sets expectations for data quality; they are best used to contextualise single-arm results and to design, not replace, randomised confirmatory trials.","asOf":"2026-09-09","wikipedia":"https://en.wikipedia.org/wiki/Synthetic_control_method","links":[{"label":"FDA guidance: considerations for the design and conduct of externally controlled trials","url":"https://www.fda.gov/regulatory-information/search-fda-guidance-documents/considerations-design-and-conduct-externally-controlled-trials-drug-and-biological-products"}],"tags":[],"related":["single-arm","real-world-evidence","control-arm","accelerated-approval","bayesian-trial-design","trial-failure-modes","registry-based-trial"],"cancers":[],"sections":["drug-discovery"],"technologies":["oncology-real-world-data","flatiron-health"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":[],"trials":["nmtrc003","l-mind","act-iv","convert"],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"Trials"},"route":"/terms/external-control-arm/","neighbours":{"term":[{"id":"accelerated-approval","kind":"term","name":"Accelerated approval","route":"/terms/accelerated-approval/"},{"id":"bayesian-trial-design","kind":"term","name":"Bayesian trial design","route":"/terms/bayesian-trial-design/"},{"id":"control-arm","kind":"term","name":"Control arm and comparator (investigator's choice)","route":"/terms/control-arm/"},{"id":"real-world-evidence","kind":"term","name":"Real-world evidence","route":"/terms/real-world-evidence/"},{"id":"registry-based-trial","kind":"term","name":"Registry-based randomised trial","route":"/terms/registry-based-trial/"},{"id":"single-arm","kind":"term","name":"Single-arm trial","route":"/terms/single-arm/"},{"id":"trial-failure-modes","kind":"term","name":"Why trials fail: underpowered, wrong endpoint, control arm drift, subgroup fishing, crossover","route":"/terms/trial-failure-modes/"}],"section":[{"id":"drug-discovery","kind":"section","name":"Drug Discovery Platforms","route":"/fronts/drug-discovery/"}],"technology":[{"id":"oncology-real-world-data","kind":"technology","name":"Oncology EHR and real-world data platforms","route":"/technologies/oncology-real-world-data/"}],"company":[{"id":"flatiron-health","kind":"company","name":"Flatiron Health (Roche)","route":"/companies/flatiron-health/"}],"trial":[{"id":"act-iv","kind":"trial","name":"ACT IV","route":"/trials/act-iv/"},{"id":"convert","kind":"trial","name":"CONVERT","route":"/trials/convert/"},{"id":"l-mind","kind":"trial","name":"L-MIND","route":"/trials/l-mind/"},{"id":"nmtrc003","kind":"trial","name":"NMTRC003/003B (DFMO maintenance)","route":"/trials/nmtrc003/"}]}}