Why This Study Matters
Detection of circulating tumor DNA (ctDNA) after definitive treatment for early breast cancer — termed molecular residual disease, or MRD — is strongly prognostic of recurrence and can precede clinical relapse by up to 15 months. Most validated MRD assays are tumor-informed, meaning they require sequencing a patient's own tumor tissue to design a personalized panel before ctDNA can be tracked in blood. That requirement is also a limitation: archival tumor tissue may be unavailable or insufficient, sequencing and panel design take time and money, and delivering bespoke, patient-specific assays at scale is logistically demanding.
A tissue-free assay — one that does not require sequencing the primary tumor — could remove that bottleneck if it can match tumor-informed accuracy. This analysis, drawn from the ctDNA surveillance period of the multicenter phase 2 c-TRAK TN study in triple negative breast cancer (TNBC), is among the first head-to-head comparisons of a tissue-free assay against two tumor-informed comparators in a real-world surveillance cohort.
Study Design
This was a prognostic and exploratory analysis nested within the ctDNA surveillance period of c-TRAK TN (ClinicalTrials.gov identifier NCT03145961), a multicenter phase 2 study led by the Institute of Cancer Research and the Royal Marsden in London. Plasma samples were collected from participants every 3 months for up to 2 years after completion of adjuvant therapy and analyzed for ctDNA using three assay approaches, compared head-to-head:
| Assay | Approach |
|---|---|
| Tissue-free assay | Guardant Reveal, run on the Infinity targeted next-generation sequencing platform, which detects ctDNA via cancer-associated differential methylation patterns rather than patient-specific tumor variants. |
| Digital PCR (dPCR) | A patient-personalized assay tracking 1-2 tumor-specific variants, used for prospective ctDNA surveillance in the parent c-TRAK trial. |
| Multivariant tumor-informed assay (RaDaR) | A whole-exome-sequencing-powered assay tracking up to 48 variants per patient. |
Data for this analysis were drawn from a database lock on September 28, 2021, with follow-up through January 18, 2023; the analysis itself was conducted between July 2025 and May 2026. The primary objective was to assess the prognostic significance of tissue-free ctDNA detection, with recurrence-free survival by detection status as the main outcome measure.
Patient Population
The analysis included 159 patients with triple negative breast cancer at moderate to high risk of recurrence, all enrolled in the ctDNA surveillance period of c-TRAK TN. Mean age was 51.4 years (SD 11.4; range 25.0-78.0), and all participants were female. A total of 1,026 plasma samples were analyzed across the cohort, collected roughly every 3 months over a follow-up window of up to 24 months.
Primary Endpoint Results
The tissue-free assay detected ctDNA in 54 of 159 patients (34.0%). Detection was strongly and significantly associated with risk of recurrence: HR, 27.2 (95% CI, 13.7-54.2; P < .001).
Lead time versus dPCR: Among 42 patients (26%) with ctDNA detected by both the tissue-free assay and dPCR, tissue-free detection came first in 14 patients (33.3%); dPCR detection preceded tissue-free detection in zero patients. Median lead time to recurrence was 7.9 months (95% CI, 6.1-10.5) for the tissue-free assay versus 5.8 months (95% CI, 3.3-10.0) for dPCR (HR, 0.57; 95% CI, 0.34-0.95; P = .03).
Lead time versus the multivariant tumor-informed assay: Among 41 of 133 patients detected by both the tissue-free and multivariant tumor-informed assays, the tumor-informed assay detected ctDNA earlier in 12 patients (29.3%), while the tissue-free assay detected earlier in only 1 patient (2.4%). Median lead times to recurrence were 7.6 months (95% CI, 4.6-10.5) for tissue-free versus 7.1 months (95% CI, 5.7-10.0) for the multivariant tumor-informed assay (HR, 1.46; 95% CI, 0.87-2.44; P = .15) — a difference the authors report as not statistically significant.
Diagnostic accuracy by 24 months: Among 127 patients (79.9%) evaluable at 24 months (32 patients were censored or lost to follow-up before 24 months and were recurrence-free at last assessment), the tissue-free assay's sensitivity for identifying any recurrence was 84.4%, with ctDNA detected in 38 of 45 patients who relapsed. Specificity was 87.8%, positive predictive value 79.2%, and negative predictive value 91.1%. For distant recurrence specifically, sensitivity was 85.7% (24 of 28 patients).
| Diagnostic Metric (by 24 months, any recurrence) | Value |
|---|---|
| Sensitivity | 84.4% (38/45 patients with relapse detected) |
| Specificity | 87.8% |
| Positive predictive value | 79.2% |
| Negative predictive value | 91.1% |
| Sensitivity, distant recurrence only | 85.7% (24/28 patients) |
Cross-Assay Concordance
Rather than a conventional biomarker subgroup breakdown, the most clinically relevant comparative data from this analysis are the assay concordance figures — how often the tissue-free and tumor-informed methods agreed at the same blood draw.
| Comparison | Timepoints Compared | Concordant Results | Agreement Rate | Cohen's kappa |
|---|---|---|---|---|
| Tissue-free vs. dPCR | 1,005 (159 patients) | 950 | 94.5% (95% CI, 92.9%-95.9%) | 0.70 (95% CI, 0.63-0.77) |
| Tissue-free vs. multivariant tumor-informed | 809 (133 patients) | 770 | 95.2% (95% CI, 93.5%-96.5%) | 0.79 (95% CI, 0.72-0.85) |
Of the 159 patients profiled with the tissue-free assay, 26 (16.4%) did not have a multivariant tumor-informed result available — most commonly (21 of 26, 80.8%) because whole-exome sequencing of the archival tumor specimen failed, due to insufficient tumor content, DNA, identified variants, or sample contamination. This gap is itself a data point in favor of a tissue-free option: roughly one in six patients in this cohort could not be assessed by the tumor-informed method at all. The authors also found no difference in the mean plasma volume required for the two approaches (3.89 mL tissue-free vs. 3.88 mL multivariant tumor-informed; P = .21), indicating the tissue-free method is not a heavier blood-draw burden.
Safety Profile
This analysis evaluates diagnostic assay performance, not a therapeutic intervention. The published full text does not report adverse event, toxicity, or safety/tolerability data, because none apply to a comparison of blood-based ctDNA assays. Readers should note this is a biomarker/assay-comparison study, not a drug safety analysis.
Interpretation and Broader Context
A tissue-free approach has the potential to streamline clinical workflows and offer a practical alternative when an archival tumor sample is not available or inadequate to generate tumor-informed assays.
— Discussion, Cunningham et al., JAMA Oncology, 2026
The study authors frame the tissue-free approach as a way to extend MRD surveillance to patients for whom a tumor-informed assay isn't feasible. They emphasize that tissue-free detection was strongly prognostic for disease recurrence, anticipating clinical relapse by a median of 7.9 months — a lead time they describe as comparable to that reported in studies using multivariant tumor-informed approaches. At the same time, the multivariant tumor-informed assay detected ctDNA at an earlier time point in a larger share of concordantly detected patients (29.3% vs. 2.4%), suggesting it may retain an edge in absolute sensitivity even where median lead times converge.
The authors also note a key limitation: this study did not compare the tissue-free assay against whole-genome-sequencing-powered tumor-informed assays, which have even higher analytical sensitivity (limit of detection of approximately 3.45 parts per million, versus roughly 11 parts per million for the whole-exome-based comparator used here) and could plausibly show longer lead times than were observed against the whole-exome comparator in this study.
Future Directions
What's next: the authors conclude that the clinical benefit of early MRD detection and intervention remains uncertain, and call for prospective, ctDNA-guided intervention studies to establish clinical utility — trials that test whether acting on a positive tissue-free MRD result (for example, with early systemic therapy) actually improves outcomes, rather than simply detecting recurrence earlier.
In this prognostic analysis nested within the phase 2 c-TRAK TN trial, a tissue-free ctDNA assay performed comparably to costlier, sequencing-based tumor-informed assays for detecting molecular residual disease in early triple negative breast cancer — with a median lead time of 7.9 months, 84.4% sensitivity and 87.8% specificity by 24 months, and agreement rates above 94% against both tumor-informed comparators. Because roughly one in six patients in this cohort could not be assessed by the tumor-informed method due to archival tissue or sequencing failures, a validated tissue-free option could meaningfully widen access to recurrence surveillance. But detecting recurrence earlier is not the same as improving outcomes: the authors call the clinical benefit of early intervention "uncertain" and are calling for prospective, ctDNA-guided intervention trials before this approach can inform routine practice.