Skip to content
Download PDF

Circulating Nucleic Acids as Liquid Biopsies and Noninvasive Disease Biomarkers

Chapter 503 | Part 20: Emerging Topics in Clinical Medicine · Parts 19-20 – Consultative & Emerging Topics · Chapter 503

Key Clinical Points

  1. Clonal hematopoiesis of indeterminate potential (CHIP) is a major source of false-positive ctDNA findings, with prevalence approaching 100% in adults >60 years old.
  2. Donor-derived cfDNA (dd-cfDNA) serves as a highly sensitive marker for graft injury; levels rise 4–6 days before transaminase elevation and 8–15 days before biopsy confirmation of rejection in liver transplantation.
  3. In heart transplantation, a dd-cfDNA threshold of 0.25% provides a 99% negative predictive value (NPV) for acute rejection.
  4. Liquid biopsy assays are generally not optimal for detecting minimal residual disease (MRD) because ctDNA allele fractions post-treatment are typically <0.5%.
  5. Next-generation sequencing (NGS) offers high sensitivity for ctDNA detection, while amplicon-based methods (ddPCR, AS-PCR) are preferred for cost and turnaround time in early detection.
  6. Noninvasive prenatal testing (NIPT) utilizes cell-free DNA from maternal plasma to detect fetal aneuploidies (+21, +18), microdeletions, duplications, and single-gene disorders.
  7. dd-cfDNA levels vary by organ type: 5–10% in stable liver transplant recipients vs. <0.1% in heart transplant patients.
  8. The virome is highly sensitive to immunosuppressive drug use; high doses lead to dominance by Anelloviridae or torque teno viruses (TTV).
  9. ctDNA profiling can identify specific mutations to guide therapy, such as EGFR mutations for osimertinib response and KRAS mutations for sotorasib response.
  10. While promising for guiding adjuvant therapy, randomized trials demonstrating a survival advantage for early detection using liquid biopsies have not yet been performed.

DEFINITION & OVERVIEW

• Liquid Biopsy: Analysis of bodily fluids (e.g., urine, blood) for clinical use. • Metabolomics: Part of the "-omics" suite; directly connected to phenotype and sensitive to system perturbations. → Note: Requires awareness of biological/practical confounders and technical limitations. • cfDNA (Cell-free DNA): Naturally fragmented DNA in circulation, primarily from hematopoietic sources. • ctDNA (Circulating Tumor DNA): A subset of cfDNA specifically derived from tumor cells. • Other Liquid Biopsy Analytes: ◦ Exosomes (membrane-bound vesicles). ◦ cfRNA (cell-free RNA). • Sample Sources: Blood (most common), urine, feces, pleural fluid, peritoneal fluid, bronchoalveolar lavage fluid, saliva, and cerebrospinal fluid.

EPIDEMIOLOGY

• Hematologic Monitoring: Direct examination of circulating elements is standard for leukemia/lymphoma. → Note: Most human cancers do not have detectable circulating tumor cells as evidence for minimal residual disease (MRD) in the cellular compartment of the blood.

Clonal Hematopoiesis Prevalence

• CHIP (Clonal Hematopoiesis of Indeterminate Potential): Mutations in ~20 genes associated with hematologic neoplasms (>2% allelic fraction) in patients not meeting leukemia criteria. → Risk Factor: Associated with cardiovascular disease and hematologic neoplasms. → Impact on Liquid Biopsy: Major contributor to biological mutational background; can cause false-positives. → Prevalence: Increases with patient age, larger gene panels, and sensitive testing; approaches 100% in adults >60 years old. • Specific Genes Affected by CHIP: ◦ DNMT3A, TET2, ASXL1, JAK2 (associated with myeloid cell fitness). ◦ TP53: 15–41% of cfDNA mutations in this gene are attributable to CH rather than tumor tissue. • Table 1 Summary: Confirms high prevalence of DNMT3A, TET2, ASXL1, and JAK2 in myeloid cells; notes 15–41% of TP53 mutations are from CH.

Cancer Screening Statistics

• Current Challenges: High false discovery rates (~90%) and low compliance in current methods (e.g., low-dose CT for lung cancer). → Need: New methods for early detection of lung, colorectal, and breast cancers. • ctDNA as a Solution: Potential for blood-based screening via: ◦ Individual cancer system focus. ◦ Multi-analyte testing (ctDNA + proteins). ◦ Broad (dd-cfDNA) multicancer early detection (MCED) assays (utilizing mutations, tissue-specific methylation, cfDNA fragmentation profiles, and other features).

ETIOLOGY & PATHOPHYSIOLOGY

• Tumor Shedding: Release of ctDNA into circulation via apoptosis or necrosis. • Biological Background: Mutations from non-tumor tissues (e.g., clonal hematopoiesis) can confound detection. • Tumor Genotype-Informed Analysis: → Strategy: Profile tumor tissue first to identify specific mutations, then track those specific mutations in post-treatment blood. → Benefit: Reduces false positives from background noise and requires lower blood volumes.

Tumor Shedding Mechanisms

• Circulating Tumor Cells (CTCs): Extravasated tumor cells in bloodstream. → Note: Not the primary focus of cfDNA analysis but part of the broader liquid biopsy landscape. • Exosomes: Membrane-bound vesicles released by tumor cells. → Utility: Used to interrogate proximally associated anatomic compartments via various fluids (urine, feces, etc.).

Clonal Hematopoiesis Pathogenesis

• Mechanism: Hematopoietic stem cells acquire mutations during aging. → Result: Variants found in both cfDNA and circulating peripheral blood leukocytes. → Clinical Trap: Mutations from CHIP can masquerade as ctDNA, leading to false positives.

Transplant Rejection Biology

• Concept: Transplantation is a "genome transplant." • dd-cfDNA (Donor-derived cfDNA): → Source: Derived from both recipient tissues and the donated organ. → Correlation: Elevated levels reflect graft injury due to acute rejection or other damage. → Organ Variation: ◦ Liver: 5–10% in stable recipients. ◦ Heart: <0.1% in patients. → Prognostic Value: High early dd-cfDNA (within first 3 months) predicts chronic allograft dysfunction; high dd-cfDNA at discharge predicts dysfunction at 1 year.

CLINICAL FEATURES

• Monitoring Dynamics: Quantitative changes in ctDNA used to monitor response, similar to functional imaging. → Critical Factors: Tumor histology, treatment setting (frontline vs. relapsed), timing of assessment, and assay sensitivity/specificity.

Oncology Clinical Presentation

• Early Molecular Response: → Example: 100-fold reductions (2-log) in ctDNA after one cycle of induction chemotherapy in DLBCL and Hodgkin’s lymphoma. → Outcome: Strongly associated with event-free and overall survival. • Genomic Profiling: ◦ Whole human genome profiling. ◦ Targeted subregions (hybridization affinity capture or locus-specific amplicons).

Transplantation Clinical Features

• Acute Rejection Detection: dd-cfDNA levels increase significantly during acute rejection and correlate with severity. → Sensitivity: Detected weeks to months prior to biopsy confirmation. → Differentiation: Higher levels associated with antibody-mediated rejection (AMR) compared to cellular (T-cell-mediated) rejection; different fragment types/lengths may distinguish the two.

Infection Monitoring

• Virome Sensitivity: Highly sensitive to immunosuppressive drug use. → High Dose Effect: Leads to dominance by Anelloviridae or torque teno viruses (TTV). → Diagnostic Utility: cfDNA sequencing allows for "unbiased diagnosis" of opportunistic infections in immunocompromised patients.

DIFFERENTIAL DIAGNOSIS

• CHIP vs. Tumor Mutations: → Differentiation Strategy: Direct genotyping of peripheral blood leukocytes to identify and exclude mutations arising from CHIP. • Rejection vs. Infection vs. Ischemia: → Differentiation Strategy: Use dd-cfDNA to identify graft injury; note that in kidney transplants, dd-cfDNA may be elevated due to pyelonephritis (ischemia/infection) rather than rejection alone.

DIAGNOSTIC APPROACH

  1. ctDNA Assay Selection: • Step 1: Determine requirement for sensitivity vs. speed. • Option A: Next-generation sequencing (NGS) → High sensitivity for detection. • Option B: Amplicon-based methods (ddPCR, AS-PCR) → Preferred for cost and turnaround time in early detection.
  2. dd-cfDNA Monitoring (Transplant): • Step 1: Measure dd-cfDNA levels in circulation. • Step 2: Evaluate against clinical thresholds. • Heart Transplant: ≥0.25% → High sensitivity for severe rejection; 99% NPV for acute rejection. • Timing Analysis: • Detection 4–6 days before transaminase rise → Early warning of graft injury. • Detection 8–15 days before biopsy confirmation → Opportunity to adjust immunosuppression.
  3. Noninvasive Prenatal Testing (NIPT): • Step 1: Analyze cell-free DNA from maternal plasma. • Targets: Fetal aneuploidies (+21, +18), microdeletions, duplications, and single-gene disorders.

MANAGEMENT & TREATMENT

  1. Oncology Treatment Selection: • Step 1: Identify specific mutations via ctDNA profiling. • Action A: Detect EGFR mutations → Inform osimertinib response. • Action B: Detect KRAS mutations → Inform sotorasib response.
  2. Transplantation Management: • Step 1: Monitor dd-cfDNA levels as a marker of graft injury. • Action: If rising levels detected early → Prompt adjustment/augmentation of immunosuppressive therapy to halt damage before clinical rejection occurs.
  3. Monitoring Response: • Step 1: Assess ctDNA reduction after induction chemotherapy. • Threshold: 100-fold (2-log) reduction → Define early molecular response in DLBCL and Hodgkin's.

PROGNOSIS & COMPLICATIONS

• Relapse Prediction: → Detection of "Subclone 3" (emergent resistance) before clinical progression. → Identification of minimal residual disease (MRD) to guide adjuvant therapy. • Graft Dysfunction Risk: → Lung: High average dd-cfDNA levels in first 3 months → High risk for chronic allograft dysfunction and failure. → Kidney: High dd-cfDNA at hospital discharge → Predicts graft dysfunction at 1 year.

SPECIAL CONSIDERATIONS

• Prenatal Care: → Use of NIPT for noninvasive detection of fetal genetic disorders. → Advantage: Avoids invasive procedures to identify aneuploidies or single-gene disorders. • Immunocompromised Patients: → Use of cfDNA sequencing for unbiased diagnosis of opportunistic infections (e.g., identifying Anelloviridae dominance under high immunosuppression).

KEY PEARLS & CLINICAL TRAPS

• CHIP Trap: Always consider age; in patients >60, nearly 100% of ctDNA samples may contain CHIP mutations (especially DNMT3A, TET2, ASXL1, JAK2). • dd-cfDNA Sensitivity: It is a highly sensitive marker for graft injury, often preceding clinical signs or biochemical changes (transaminases) by days to weeks. • Heart Transplant Threshold: 0.25% dd-cfDNA → 99% NPV for acute rejection. • Virome Dynamics: TTV load is inversely related to immune response; high TTV correlates with higher immunosuppression and progression to CMV disease.