On April 11, 2025, Nature Methods published a study in which researchers combined low-cost, deep whole-genome sequencing (WGS) with duplex error correctionto reliably detect tumor DNA in blood at 1 part per million (ctDNA). This marks an important threshold for early detection and post-treatment recurrence monitoring in cancer.

Why Is It Needed? — A Turning Point for Liquid Biopsy

Liquid biopsy detects circulating tumor DNA (ctDNA) in a blood sample, enabling early cancer detection, minimal residual disease (MRD) and treatment response monitoring. However, ctDNA is often present at very low fractions ; conventional sequencing errors can hide this signal in noise. The new method both dramatically reduces the error rate and scans the entire genome to strengthen the signal.

🧬 What Is the Method? — Deep WGS + Duplex Error Correction

Deep WGS (~120×): High coverage across the whole genome using a new, low-cost platform (Ultima).
Duplex correction: Matches information from DNA’s two strands to eliminate random read errors.
Error rate: ~7.7 × 10⁻⁷ (fewer than 1 error per million).
Sensitivity: ctDNA can be detected in the parts-per-million (ppm) range (10⁻⁶–10⁻⁷).
No tumor data are required for operation (tumor-agnostic); when available, tumor signatures further strengthen tumor-informed analysis.

📊 Summary in Numbers

Coverage depth: ~120× WGS
Lowest ctDNA detection: ppm level (10⁻⁶ – 10⁻⁷)
Error rate: ~7.7 × 10⁻⁷ (duplex WGS)
Cancer types: Successfully demonstrated in melanoma and urothelial carcinoma
Additional feature: APOBEC (bladder), UV (melanoma) and platinum chemotherapy mutational signatures could be monitored through blood

🎯 How Can It Help Clinically?

MRD and recurrence monitoring: After surgery/chemotherapy/immunotherapy, ppm level ctDNA detection provides an early warning; it may signal disease before imaging findings.
Response monitoring: Circulating ctDNA decreases may indicate a biochemical response, while increases may indicate progression risk (interpreted in the clinical context).
Signature-based interpretation: UV/APOBEC/platinum signatures allow etiology, treatment effects and possible resistance dynamics to be monitored through blood.
Analysis without tumor tissue: Using only a blood sample when biopsy is impossible or dangerous enables meaningful molecular monitoring.
Cost-effective depth: Low-cost deep WGS + duplex correction offer the potential for routine use.
Practical reporting: ctDNA fraction (ppm), trend (↑/↓/↔), detected signature and clinical recommendation (example: “Repeat measurement in 3–4 weeks; early imaging if symptomatic”).

🩺 Implementation Workflow (Suggested)

Define the indication: Postoperative / post-chemotherapy/immunotherapy monitoring, suspected progression, cases unsuitable for biopsy, early screening research.
Sampling & preanalytics: Plasma cfDNA, rapid centrifugation and double-stranded (duplex) library preparation.
Sequencing: Deep WGS (~120×) + duplex error correction.
Analysis: ctDNA fraction (ppm), Z-score, mutational signatures (UV/APOBEC/platinum) and clonal hematopoiesis filtering.
Decision:
- ctDNA ↓ and no symptoms → routine follow-up interval (e.g., 8–12 weeks).
- ctDNA ↑ or a new pathogenic signature → repeat testing within 3–4 weeks ± early imaging.
- Persistent ↑ (≥2 consecutive measurements) → imaging for progression and tumor board review.
- Discordant (ctDNA ↑, imaging ↔) → repeat measurement at a short interval + additional targeted imaging.

Note: Thresholds should follow institutional protocols; ctDNA alone is insufficient for a treatment change decision—it must be interpreted alongside clinical findings, laboratory data and imaging.

🕵️‍♂️ Early Detection

Detecting low-fraction ctDNA at the ppm level; research screening in high-risk groups.

📉 MRD / Recurrence Monitoring

After surgery/chemotherapy/immunotherapy, an early recurrence signal; intervals may be extended if negative, while positive results prompt close monitoring/imaging.

🎯 Treatment Response

ctDNA trend analysis shows biochemical response; early review if discordant with symptoms.

🧬 Mutational Signatures

UV/APOBEC/platinum signatures reveal biology and treatment effects and contribute to clinical classification.

💉 Analysis Without Tumor Tissue

Even when biopsy is impossible, a blood sample enables molecular monitoring; decisions require multidisciplinary assessment.

⚠️ Cautions and Limitations

Preanalytical process errors (plasma processing, library preparation) may affect sensitivity.
Clonal hematopoiesis and other nontumor variants must not be misinterpreted; duplex correction reduces this risk, but clinical context is essential.
Early screening requires prospective validation in large populations.

🌟 Looking Ahead

Error-corrected deep WGS makes early, sensitive cancer monitoring through blood tests accessible. In the near future, oncology practice may see MRD monitoring with a routine blood test, signature-based treatment decision support and personalized follow-up intervals become possible.

🔗 Source

Cheng AP, Widman AJ, Arora A, et al. Error-corrected flow-based sequencing at whole-genome scale and its application to circulating cell-free DNA profiling. Nature Methods, 2025. Article link.

Menu

Detecting Tumor DNA at 1 Part per Million in Blood With Error-Corrected Whole-Genome Sequencing

Why Is It Needed? — A Turning Point for Liquid Biopsy

🧬 What Is the Method? — Deep WGS + Duplex Error Correction

📊 Summary in Numbers