Follow-up after treatment for early breast cancer relies on clinical review and regular mammography, because randomised trials that added routine scans and blood tests to find asymptomatic metastases sooner do not produce a gain in overall survival (Cochrane 2016). Circulating tumour DNA has reopened that question. A blood test sensitive enough to detect tumour DNA months before relapse could, in principle, allow further treatment while the remaining disease is still microscopic, and that possibility has drawn intense interest from clinicians, trialists and the diagnostics industry.
Several obstacles separate the idea from routine care. After curative treatment tumour DNA circulates in minute quantities, the most sensitive assays require a sample of the patient’s original tumour, which is not always available, and no trial has yet shown that treating relapse earlier improves survival. A study published in JAMA Oncology in August 2026 addresses the second of these obstacles by testing an assay that works from blood alone, and its findings are best read against all three.
What is molecular residual disease, and how does circulating tumour DNA reveal it?
Circulating tumour DNA (ctDNA) consists of short fragments of DNA released into the bloodstream by cancer cells, where they mix with a far larger quantity of cell-free DNA shed mainly by blood cells. After surgery and chemotherapy, scans may show no cancer while small deposits persist elsewhere in the body, and the detection of ctDNA in that setting is termed molecular residual disease (MRD).
Molecular residual disease is closely linked to later relapse. In a UK cohort of 101 patients with early breast cancer, ctDNA detected during follow-up carried a hazard ratio for relapse of 25.2, and in a combined cohort of 144 patients detection preceded clinical relapse by a median of 10.7 months (JAMA Oncol 2019).
Why is ctDNA so difficult to detect after treatment for early breast cancer?
The first difficulty with ctDNA after curative treatment is quantity. In the TRAK-ER study of hormone receptor-positive breast cancer, positive samples taken after the first surveillance test had a median allele fraction of 0.0135%, roughly one tumour-derived fragment among 7,400 (ESMO Breast 2026). An assay has to find a signal at that level in a few millilitres of plasma, and must do so repeatedly over years of follow-up, since each false positive leads to staging scans and an anxious wait.
Most assays in current breast cancer studies reach this sensitivity by being tumour-informed: the patient’s tumour is sequenced to identify mutations unique to that cancer, and a bespoke test is then built to look for those mutations in blood. The c-TRAK TN trial in triple negative breast cancer (TNBC) used digital polymerase chain reaction (dPCR) assays of this kind, tracking one or two mutations per patient (Ann Oncol 2023).
This dependence on tissue carries a cost. Archival samples may contain too little tumour DNA, and every patient needs a custom assay designed before surveillance can begin. In TRAK-ER, assay design failed in 178 of 1,104 patients (16.1%), and those patients received no test at all.
Tissue-free approaches avoid the need for a tumour sample by looking for features common to cancer DNA in general. Earlier versions searched for common cancer mutations and were hampered by clonal haematopoiesis, the age-related build-up of mutations in blood-forming cells that shed DNA into plasma. In one high-depth plasma sequencing study, 81.6% of mutations found in people without cancer had features consistent with clonal haematopoiesis (Nat Med 2019).
Has detecting breast cancer relapse earlier with ctDNA been shown to help patients?
No randomised trial has yet shown that starting treatment at molecular relapse improves outcomes in breast cancer compared with starting it when relapse becomes clinically apparent, and the trials conducted so far have found that a positive test often arrives too late for a treatment window to exist.
In c-TRAK TN, 23 of the 32 patients allocated to intervention after a positive dPCR test already had metastases on staging scans, and none of the five who began pembrolizumab cleared their ctDNA (Ann Oncol 2023). In TRAK-ER, 45 of the 105 patients with ctDNA detected (42.9%) already had recurrent disease when the first positive result came back.
Professional guidance follows this evidence. The European Society for Medical Oncology states that MRD detection cannot be recommended in routine practice because no evidence yet shows that it improves treatment decisions (Ann Oncol 2022), and the 2026 American Society of Clinical Oncology follow-up guideline does not recommend ctDNA for recurrence monitoring outside a clinical trial (J Clin Oncol 2026).
What did the c-TRAK TN analysis of a tissue-free ctDNA assay conclude?
Cunningham and colleagues applied a tissue-free assay, Guardant Reveal, which reads DNA methylation (the chemical tagging of DNA that governs gene activity), to plasma samples banked during c-TRAK TN surveillance in women with TNBC, and compared its results with two tumour-informed tests run on the same samples: the dPCR assay used in the trial and a more sensitive assay built from exome sequencing of each tumour (JAMA Oncol 2026).
Detection by the tissue-free assay was strongly associated with subsequent relapse. It tended to detect ctDNA earlier than the dPCR assays, and its median warning before relapse was similar to that of the exome-based tumour-informed assay. The tumour-informed assay was nonetheless more often first to detect, and found some cases at very low ctDNA levels that the tissue-free assay missed, so the authors advise against using the tissue-free approach to withhold treatment from patients whose ctDNA is undetectable unless a tumour-informed assay cannot be made. They conclude that the results support tissue-free MRD testing within clinical trials, particularly for patients without usable tumour tissue. The full data are available in the open-access paper.
These conclusions carry several qualifications. The analysis was retrospective and exploratory, drew on a single trial with modest numbers of relapses, and its comparison of warning times was not designed to show that the two assays are equivalent. Patients did not have routine imaging, so some may already have had occult metastases when ctDNA first appeared. TNBC also releases relatively large amounts of tumour DNA into the blood, and discussing the findings at ESMO Breast Cancer 2026, Dr Stefania Morganti of the Dana-Farber Cancer Institute noted that tissue-free sensitivity in lower-shedding hormone receptor-positive disease is unknown. The work was supported in part by Guardant Health, which makes the tissue-free assay, although the funders had no role in its design, analysis or the decision to publish.
Could ctDNA surveillance be implemented in NHS Scotland?
ctDNA surveillance is not ready for routine use in NHS Scotland, and the tissue-free result alters only one part of that position. It offers a way around tumour sequencing and bespoke assay design, the step at which tumour-informed pathways lose about one patient in six, but leaves unanswered the question of clinical benefit on which everything downstream depends.
A service would also need analytical validation of any assay at tumour fractions near 0.01%, and local capacity for this service does not currently exist (Scottish Government 2024). Imaging and oncology capacity would have to absorb every positive result, since each one triggers staging scans and a discussion of treatment. Evaluating such a service with Scotland’s linked routine data would meet a further gap: cancer registries do not routinely record recurrence, so relapse would have to be derived from treatment and hospital records using a validated algorithm (Curr Oncol 2022).
The economic case is similarly unresolved. We found no published economic evaluation of ctDNA surveillance in early breast cancer, and the TRAK-ER yield shows what any such evaluation would have to absorb: of 1,104 patients who entered assay design, about 60 reached a positive result with no visible disease and could have been offered treatment at molecular relapse. A tissue-free assay would reduce losses at the first step of that pathway but not at the last.
For now, the practical role of tissue-free ctDNA in Scotland lies in research, including Scottish participation in the trials that will settle clinical benefit. The TRAK-ER (NCT04985266) and DARE (NCT04567420) trials are testing whether treating molecular relapse in hormone receptor-positive breast cancer delays or prevents recurrence, and tissue-free assays now need direct comparison with tumour-informed assays in that lower-shedding disease.
References
- Moschetti I, Cinquini M, Lambertini M, Levaggi A, Liberati A. Follow-up strategies for women treated for early breast cancer. Cochrane Database Syst Rev. 2016;(5):CD001768. doi:10.1002/14651858.CD001768.pub3
- Garcia-Murillas I, Chopra N, Comino-Méndez I, Beaney M, Tovey H, Cutts RJ, et al. Assessment of molecular relapse detection in early-stage breast cancer. JAMA Oncol. 2019;5(10):1473-8. doi:10.1001/jamaoncol.2019.1838
- Cunningham N, et al. ctDNA detection rates during surveillance in high-risk HR+/HER2 negative breast cancer from the TRAK-ER study. ESMO Breast Cancer 2026, Abstract 1O. Reported in ESMO Daily Reporter, 7 May 2026. dailyreporter.esmo.org
- Turner NC, Swift C, Jenkins B, Kilburn L, Coakley M, Beaney M, et al. Results of the c-TRAK TN trial: a clinical trial utilising ctDNA mutation tracking to detect molecular residual disease and trigger intervention in patients with moderate- and high-risk early-stage triple-negative breast cancer. Ann Oncol. 2023;34(2):200-11. doi:10.1016/j.annonc.2022.11.005
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- Cunningham N, Cutts RJ, Swift C, Coakley M, Sritharan P, Dunne K, et al. Tissue-free vs tumor-informed ctDNA assays for molecular residual disease detection in early triple negative breast cancer. JAMA Oncol. Published online 13 August 2026. doi:10.1001/jamaoncol.2026.2833
- Scottish Government. Genomic medicine strategy 2024 to 2029, section 9: timely and equitable access to genetic testing. gov.scot
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