{"entity":{"id":"idea-tr2-ctdna-futility-gates","kind":"idea","name":"Kill combination arms early using circulating tumour DNA, before waiting for scans","aka":[],"tldr":"A blood test at six weeks can show whether a treatment is doing anything. Trials should use it to drop failing combinations fast and move patients on.","summary":"Molecular response (ctDNA clearance or fall below a threshold at 6 to 9 weeks) correlates with progression-free and overall survival across several tumour types and drug classes. Platform trials could use pre-specified ctDNA futility rules at 20 patients per arm to stop non-performing combinations months earlier than radiological endpoints allow.","asOf":"2026-09-08","links":[{"label":"Bottleneck evidence (Too many combinations to test): Palmer & Sorger, Combination cancer therapy can confer benefit via patient-to-patient variability without drug additivity or synergy (Cell 2017)","url":"https://doi.org/10.1016/j.cell.2017.11.009"}],"tags":[],"related":["guardant-health","natera","idea-cd8-pet-io"],"cancers":[],"sections":[],"technologies":["liquid-biopsy"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["ctdna","recist","pfs"],"trials":[],"people":[],"bottlenecks":["b-combination-space","b-trial-design"],"keyPapers":["paper-palmer-cell"],"journals":[],"dependsOn":[],"notes":[],"hypothesis":"Arms stopped for ctDNA futility would, had they continued, have failed their radiological primary endpoint in at least 85% of cases; adopting the rule increases the number of arms tested per year by at least 50%.","rationale":"Several studies show early ctDNA dynamics predict RECIST response and survival on immunotherapy and targeted therapy. Futility, unlike efficacy, needs only a reliable negative predictor.","test":"Run the rule in shadow mode in an existing platform for two years, recording what would have been stopped and comparing with final radiological results.","maturity":"early-clinical","actor":"research","cost":"medium","horizonYears":3},"route":"/ideas/idea-tr2-ctdna-futility-gates/","neighbours":{"company":[{"id":"guardant-health","kind":"company","name":"Guardant Health","route":"/companies/guardant-health/"},{"id":"natera","kind":"company","name":"Natera","route":"/companies/natera/"}],"idea":[{"id":"idea-cd8-pet-io","kind":"idea","name":"CD8 PET to stop or switch immunotherapy early","route":"/ideas/idea-cd8-pet-io/"},{"id":"idea-tr2-bandit-allocation","kind":"idea","name":"Let the trial learn: response-adaptive allocation across many combination arms","route":"/ideas/idea-tr2-bandit-allocation/"}],"technology":[{"id":"liquid-biopsy","kind":"technology","name":"Liquid biopsy (ctDNA)","route":"/technologies/liquid-biopsy/"}],"term":[{"id":"ctdna","kind":"term","name":"Circulating tumour DNA (ctDNA)","route":"/terms/ctdna/"},{"id":"pfs","kind":"term","name":"Progression-free survival (PFS)","route":"/terms/pfs/"},{"id":"recist","kind":"term","name":"RECIST","route":"/terms/recist/"}],"bottleneck":[{"id":"b-combination-space","kind":"bottleneck","name":"Too many combinations to test","route":"/bottlenecks/b-combination-space/"},{"id":"b-trial-design","kind":"bottleneck","name":"Trial design, endpoints and cost","route":"/bottlenecks/b-trial-design/"}],"paper":[{"id":"paper-palmer-cell","kind":"paper","name":"Combination Cancer Therapy Can Confer Benefit via Patient-to-Patient Variability without Drug Additivity or Synergy","route":"/key-papers/paper-palmer-cell/"}]}}