Standard liquid biopsy technology may be leaving a significant number of pancreatic cancer patients in a false sense of reassurance — classified as disease-free when sensitive testing would show otherwise. A new prospective study from Northwestern University, published in Clinical Cancer Research in July 2026, makes that case with striking clarity: a highly targeted blood test detected residual cancer in nearly four times as many patients as standard next-generation sequencing at the time of diagnosis.

The study tested KRAS-directed digital droplet PCR (ddPCR) against standard tumor-agnostic NGS in 106 patients with localised pancreatic ductal adenocarcinoma (PDAC) — one of the deadliest solid tumours, with five-year survival rates below 15% even when caught early enough for surgery. The results illuminate a detection gap that may have real clinical consequences as KRAS-targeted therapies enter the treatment landscape.

Source: Chawla et al., Clinical Cancer Research, 2026

What Is ctDNA — and Why Does Sensitivity Matter?

Circulating tumour DNA (ctDNA) is genetic material shed by cancer cells into the bloodstream. Testing for ctDNA in blood — a "liquid biopsy" — can detect active cancer without a tissue sample, making it particularly useful for monitoring residual disease after treatment, assessing response to chemotherapy, and predicting recurrence.

But not all ctDNA tests are equal in their sensitivity. The two main approaches are:

Next-generation sequencing (NGS) — scans broadly across many gene mutations simultaneously. This makes NGS versatile for profiling unknown mutations, but less sensitive for detecting very small quantities of tumour DNA, particularly in cancers like PDAC where ctDNA levels in blood can be extremely low.

Digital droplet PCR (ddPCR) — partitions a blood sample into tens of thousands of individual reaction chambers, each containing a single DNA molecule, and targets specific pre-defined mutations with exceptional precision. For PDAC, where KRAS mutations are present in approximately 90% of tumours, ddPCR can be directed at the three most common variants — KRAS G12D, G12V, and G12R — with sensitivity that standard NGS cannot match.

The question this study set out to answer: does that sensitivity difference translate into clinically meaningful prognostic information?

The Study: Design and Patient Population

Chawla and colleagues prospectively enrolled 106 patients with localised (non-metastatic) PDAC and collected blood samples at three timepoints:

At diagnosis — before any treatment commenced · After neoadjuvant chemotherapy — typically FOLFIRINOX or gemcitabine/nab-paclitaxel · Following surgical resection — pancreaticoduodenectomy (Whipple procedure) in most cases

Each sample was analysed by both methods: a commercially available tumor-agnostic NGS ctDNA panel (of the type already used in some clinical centres), and a research-grade ddPCR assay targeting KRAS G12D, G12V, and G12R. Researchers then followed patients for survival outcomes, allowing them to map ctDNA positivity against clinical trajectory.

Results: The Detection Gap at Every Timepoint

The difference in detection rates between the two methods was substantial and consistent across all three blood draw timepoints:

65% ddPCR Detection at Diagnosis vs 17% by standard NGS — a 3.8× detection advantage
60% ddPCR Positive After Chemo NGS detected only 4.5% at this stage
56% ddPCR Positive Post-Surgery NGS detected residual disease in only 8.5% post-resection

The pattern is consistent and sobering: at every stage of treatment, from initial presentation through chemotherapy to post-surgical assessment, ddPCR continued to identify KRAS-mutant ctDNA in a majority of patients that NGS classified as negative.

Side-by-Side: ddPCR vs Standard NGS in Localised PDAC

Timepoint Standard NGS Detection KRAS ddPCR Detection Detection Advantage
At diagnosis 17% 65% 3.8× more patients detected
After neoadjuvant chemo 4.5% 60% 13× more patients detected
Following surgical resection 8.5% 56% 6.6× more patients detected

The post-chemotherapy gap is particularly striking: by the time patients have completed systemic treatment and are about to proceed to surgery, standard NGS shows almost no detectable disease (4.5%), while ddPCR continues to identify active KRAS-mutant ctDNA in 60% of the same cohort. If ctDNA reflects biologically active residual disease, this suggests that standard NGS is offering false reassurance at a critical treatment decision point.

Three Survival Tiers: What ctDNA Status Predicts

The prognostic implications are where the clinical story becomes most compelling. When the researchers mapped ctDNA results onto patient survival outcomes, three clearly differentiated risk groups emerged:

ctDNA Status Risk Tier Median Overall Survival
Positive by both NGS + ddPCR High Risk ~11 months
Negative by NGS, positive by ddPCR Intermediate Risk ~27 months
Negative by both NGS + ddPCR Lower Risk ~41 months

The intermediate-risk group — patients negative by NGS but positive by ddPCR — is the critical clinical insight here. These patients would have been classified as having no detectable residual disease under standard care, yet their actual survival outcome (27 months) was substantially worse than truly ctDNA-negative patients (41 months). Under current practice, they would receive no additional intervention or surveillance intensification based on their liquid biopsy result. Under ddPCR-informed care, they could be flagged for closer monitoring or enrolled in biomarker-driven trials.

"We showed that a highly sensitive KRAS-directed assay identifies a substantial group of patients with biologically aggressive disease who would have been considered ctDNA-negative by standard NGS alone. Today, that information can help inform multidisciplinary discussions, surveillance, and clinical trial selection."

— Akhil Chawla, MD, Surgical Oncologist, Robert H. Lurie Comprehensive Cancer Center, Northwestern University

The KRAS Therapy Connection

The timing of this study is not incidental. In June 2026 — just weeks before this paper appeared — the Phase 3 RASolute 302 trial reported that daraxonrasib, a pan-RAS inhibitor, nearly doubled overall survival compared with chemotherapy in patients with previously treated metastatic pancreatic cancer.

KRAS inhibition has arrived in pancreatic cancer, after years of KRAS being considered "undruggable." The implication: accurate KRAS ctDNA detection is no longer purely prognostic — it could become the biomarker that directs who receives these agents in future perioperative trial designs. A patient who appears ctDNA-negative by NGS but harbours KRAS-mutant circulating DNA by ddPCR is exactly the patient who might benefit from KRAS-targeted therapy — if prospective trials confirm that acting on that information changes outcomes.

Expert Debate: Promising Tool or Practice-Ready Test?

Commentators who reviewed the findings for Medscape Medical News were cautiously optimistic — but emphasised a critical distinction between a prognostic biomarker and an actionable clinical assay.

Clinical Caution

"Greater sensitivity for minimal residual disease detection absolutely has the potential to change management. But I would say it's still too early to call this routine practice-changing. We don't yet know that changing therapy based on ddPCR positivity improves survival. I would not change standard treatment solely on the basis of this assay today." — Mark Ashamalla, MD, Chief of Radiation Oncology, Episcopal Health Services

This is a crucial distinction in oncology. A test that predicts outcome does not automatically justify changing treatment based on its result — that requires a prospective interventional trial in which patients are randomised according to ddPCR status. No such trial has yet reported. The field is in the evidence-generation phase, not the practice-change phase.

Where Ashamalla and Chawla agree: ddPCR has immediate value in risk-adapted surveillance, multidisciplinary treatment planning discussions, and as an enrichment biomarker for clinical trial design. Patients with ddPCR-positive disease after surgery are ideal candidates for perioperative intervention trials — and identifying them accurately matters enormously for enrolment quality.

What This Means for Oncology Practice — Right Now

The researchers were careful to position ddPCR as a complement to, rather than a replacement for, standard NGS. NGS provides broad mutational profiling that has independent clinical utility — particularly for identifying targetable variants beyond KRAS. The practical message is that a negative NGS ctDNA result should not, on its own, be taken as a biologically low-risk signal in localised PDAC.

For the clinical oncology community, several near-term implications are already clear:

Risk stratification is improved. Three survival-differentiated patient groups can now be defined using combined NGS + ddPCR testing, which is not possible with NGS alone. This can meaningfully inform counselling, surveillance intervals, and multidisciplinary team discussions.

Trial eligibility can be sharpened. Biomarker-enriched perioperative trials that include ddPCR-positive patients regardless of NGS status will capture a higher-risk, biologically meaningful population — improving statistical power and trial efficiency.

The "KRAS-negative by NGS" problem is named. This study provides evidence to challenge a common clinical assumption: that a clean standard ctDNA panel means low residual disease burden. In PDAC, it may not.

What Happens Next?

Chawla was explicit about the research gap that remains: "Our study establishes that higher-sensitivity ctDNA testing improves risk stratification. A critical question is whether acting on that information improves patient outcomes. The next step is a prospective biomarker-directed clinical trial."

The most logical next step is a Phase II or III trial randomising ddPCR-positive, NGS-negative patients to intensified perioperative therapy (potentially including a KRAS inhibitor or intensified chemotherapy) versus standard care, with overall survival as the primary endpoint. If such a trial demonstrates that treatment guided by ddPCR positivity improves outcomes, this assay could become a standard component of localised PDAC management within the next five to seven years.

If You or a Family Member Has Pancreatic Cancer: Questions to Ask Your Team

  • Is ctDNA testing available at this centre, and would it be appropriate at my stage of treatment?
  • What kind of ctDNA assay is being used — NGS, ddPCR, or another approach?
  • Are there any clinical trials open that use ctDNA results to guide treatment decisions?
  • If my standard ctDNA test is negative, does that mean there is no residual disease, or could a more sensitive test show something different?
  • What is my surveillance plan after surgery — how frequently will I be scanned, and what would trigger a change in approach?
KM
KCLG Medical Editorial Team
GCP-certified CRO · Oncology & Haematology Clinical Trials · Oak Brook, IL · Updated quarterly

Frequently Asked Questions

What is ctDNA testing and how is it used in pancreatic cancer?
Circulating tumour DNA (ctDNA) is tumour-derived DNA shed by cancer cells into the bloodstream. In pancreatic cancer, ctDNA testing — a "liquid biopsy" — can detect cancer signals without a tissue sample. It is used to assess residual disease after surgery, monitor treatment response, and predict recurrence risk. Standard approaches vary in sensitivity, and not all assays are equally effective at finding low-level disease.
What is the difference between ddPCR and NGS for ctDNA testing?
NGS scans broadly across many gene mutations simultaneously — versatile but less sensitive for detecting small amounts of tumour DNA. Digital droplet PCR (ddPCR) targets specific known mutations — in pancreatic cancer, usually KRAS G12D, G12V, and G12R — and counts individual DNA molecules with extremely high precision. This makes ddPCR far more sensitive for minimal residual disease detection in PDAC, which is almost uniformly KRAS-driven.
Can a blood test detect whether pancreatic cancer has been fully removed after surgery?
Not definitively yet, but ctDNA testing is advancing. In this 2026 study, standard NGS detected residual disease in only 8.5% of patients post-surgery, while KRAS-targeted ddPCR found it in 56%. Patients positive by ddPCR after surgery had significantly worse outcomes — suggesting ddPCR may capture biologically active residual disease that NGS misses. However, no prospective trial has yet shown that treating based on ddPCR positivity improves survival.
What are KRAS mutations and why do they matter in pancreatic cancer?
KRAS mutations are present in approximately 90% of pancreatic ductal adenocarcinomas. The three mutations targeted in this study — KRAS G12D, G12V, and G12R — account for most KRAS alterations in the disease. This high prevalence makes KRAS an ideal liquid biopsy target. Crucially, new KRAS-targeted drugs (including pan-RAS inhibitors like daraxonrasib) are now entering clinical trials, making accurate KRAS ctDNA detection increasingly actionable.
Should I ask my oncologist about ctDNA testing for my pancreatic cancer?
It is reasonable to ask whether ctDNA testing is available and appropriate for your situation. Standard NGS-based ctDNA panels are increasingly used at major cancer centres. KRAS-targeted ddPCR is currently a research tool, though it may be accessible through clinical trial enrolment. The most important step is discussing your full monitoring plan — imaging intervals and any available biomarker-guided trials — with your multidisciplinary oncology team.
What is daraxonrasib and how does it relate to ctDNA testing in pancreatic cancer?
Daraxonrasib is a pan-RAS inhibitor — a drug that blocks signalling from mutant RAS proteins. In June 2026, the Phase 3 RASolute 302 trial showed it nearly doubled overall survival vs chemotherapy in previously treated metastatic pancreatic cancer. This makes accurate KRAS ctDNA detection increasingly relevant: tools like ddPCR that identify which patients carry active KRAS-mutant disease could help match patients to these therapies and to biomarker-enriched clinical trials.

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